“When the fullness of time had come,” explains the apostle Paul, “God sent forth his Son, born of woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons” (Gal 4:4–5). What does it mean to say that God “sent” his Son? Is this (a) the point at which the Son began his existence, conceived in the womb of Mary? Or was this (b) the point at which the Son, who had been with the Father before the world existed (John 17:5), took on flesh as the unique God-man Jesus of Nazareth (John 1:14)? Or perhaps (c) the sending occurred when the Holy Spirit descended on a regular Jewish man, Joshua ben Joseph, at his baptism, singling him out for a special mission?
The first position (a) is that of the Christadelphians, who deny the preexistence of the Son, yet also affirm that Christ is God’s Son in a miraculous way, not merely the son of Joseph. The second position (b) is that of mainstream, trinitarian Christians, who believe that the Son existed with the Father and Holy Spirit from all eternity and became incarnate at a point in time. On face value it could also be the Arian or Jehovah’s Witnesses position, for they acknowledge the prexistence of the Son, but only as the first of God’s creatures. The third position (c) is the Adoptionist position, that Christ was merely a regular human being of human parentage, declared to be the Son of God by adoption and anointing. This would be the stance of some Unitarians. What are we to make of all these different views?
Firstly, we need to acknowledge that Scripture clearly teaches that Joseph of Nazareth was not the biological father of Jesus, although Mary was indeed his mother (Matt 1:18–25; Luke 1:30–35). Although Jesus’ Sonship paves the way for our adoption as children of God, Jesus is intrinsically and definitively the Son of God by his divine origin. He is not “adopted;” we are adopted as a consequence of our association with him (Rom 8:14–17; Gal 4:4–6; Heb 2:10–13). The descent of the Spirit at Jesus’ baptism was not the point at which Jesus became the Son of God, because he was already the Son of God. It was the Father’s public acknowledgement of the Sonship of his Beloved, who already pleased him (Matt 3:16–17), and the occasion of a special anointing of the Spirit, commissioning him for his ministry and saving work.
Christadelphian pioneer Robert Roberts, however, speaks in almost adoptionist terms in his concern to show the derivative nature of the Son’s divinity. Bypassing the divine conception (which he has immediately prior argued for) he states
If [Jesus] were ‘Very God’ in his character as Son, why was it necessary he should be ‘anointed’ with spirit and power? … before his anointing, he was simply the ‘body prepared’ for the divine manifestation that was to take place through him… After the Spirit’s descent upon him, he was the full manifestation of God in the flesh.” 
Many Christadelphians today are rightly uncomfortable with this statement, because it seems to contradict Jesus’ intrinsic Sonship from conception and the fact that the worship of the Son was commanded at his birth (Heb 1:6; Luke 2:11; Matt 2:11). The Bible does not imply that Jesus did not “possess” the Spirit or was not in relationship with the Spirit prior to this descent (Apart from any other argument, he was sinless throughout these years). The descent of the Spirit “as a dove,” was a visible sign, which John the Baptist recognised as indicating Jesus to be the one “who ranks before me because he was before me,” the “Lamb of God” and the one who would in turn baptise with the Spirit (John 1:29–34). Nevertheless, it was an “anointing,” for anointing marked a commissioning, the beginning of the ministry of a prophet, priest or king and these were the roles which Jesus took up as he emerged from relative obscurity to be baptised and begin the work for which he had been sent (Acts 10:38).
Several Bible passages could be misconstrued as teaching an adoptionist Christology and these are sometimes used by Christadephians (as well as Unitarians) to deny the intrinsic divinity of the Son. Romans 1:3–4 speaks of the Son “descended from David according to the flesh… declared to be the Son of God in power according to the Spirit of holiness by his resurrection from the dead.” Yet if this is taken to literally mean that Jesus was not the Son of God until so declared, then this did not happen until his resurrection, which would negate all reference to his Sonship during his ministry and crucifixion. Rather, it must refer to the powerful declaration of his Sonship provided by his resurrection, which unequivocally declares him to have always been much more than a “mere” fleshly descendant of David (Matt 22:42–46). In several places in Acts, the apostles might at first appear to be teaching an adoptionist Christology in describing Jesus as an exalted man (Acts 2:22, 36). But Peter is here speaking to Jews and driving home that “this man” whom they rejected and crucified, well guess what? He is actually the Messiah, fully approved of God and is Lord and Christ! The proof is in his resurrection which took place before them. Yes, he has been exalted, but only after first being humbled, as Philippians 2:6–11 makes clear. He has been glorified (again) with the glory he previously had with the Father (John 17:5), and is once again rich, having become poor for our sakes (2 Cor 8:9). Hebrews 1:2 states that the Son was “appointed heir” of all things, but this in context of having created the world, upholding the universe, worshipped by angels and addressed as God.
The second point to be made is that the Son is Creator, not a created being. Scripture testifies that the Son was involved in creation (Col 1:15–17; 1 Cor 8:6; Heb 1:3, 8, 16; John 1:1–3). Although the Arian position allows for Christ to create, Arians still regarded the Son himself as a created being, placing his beginning before the creation of the world yet at a finite point in time (“there was a time when he was not”). But if the Son is a creature, it is totally inappropriate for him to be worshipped, for the worship of a created being is idolatry, no matter how exalted that created being might be (Isa 40:25–28; 42:8; 45:18; Rom 1:25; Rev 4:11). This is reinforced by the prohibition of worshiping angels (Heb 1:6–14; Rev 22:8–9) and God’s declaration that he will not share his glory with another. Only if the Son is of the Godhead can he be worshipped and can he truly be Creator, not a creature.
The third point to be made is that Scripture teaches that the Son in fact did preexist the creation and was in eternal relationship with the Father (John 1:1–2; 8:42; 17:5, 24). Jehovah’s witnesses have little problem with these verses because they merely shift the Son’s creation back in time, but this doesn’t explain the eternal relationship of love nor the intrinsic divinity of the Son or his worthiness to be worshipped alongside the Father. Christadelphians have a bigger problem; they must regard all the Scriptural evidence of the Son’s preexistence as metaphorical. They allege that these passages teach only that Christ existed beforehand in his Father’s mind and intention, not literally. In support of this they cite passages such as “He was foreknown before the foundation of the world but was made manifest in the last times for the sake of you” (1 Peter 1:20). Foreknowing (proginosko) does not necessarily exclude also existing at the time, but making manifest (phaneroo) actually does imply the prior (hidden) existence of what is now being manifest. The same word is the lynchpin of the Christadelphian doctrine of God manifestation and used in 1 Timothy 3:16 and John 17:6. But no Christadelphian would argue that God did not exist before his manifestation (phaneroo) in Christ! Another passage sometimes used is “the Lamb slain from the foundation of the world” (Rev 13:8), arguing that since the Lamb wasn’t actually slain until about 30 AD, he himself was only foreordained and did not exist before then. But the passage, which is paralleled in Rev 17:8, is actually referring to the names of those written in the book of life who are so foreordained from the foundation of the world, as per Romans 8:29–30; those he foreknew he predestined, called, justified and glorified. Whilst the Son’s redeeming work and its consequences were foreordained and not actuated until he was “sent,” the arguments for his preexistence still stand.
Scripture, in the words of Jesus himself as well as the New Testament writers, is clear that the Father sent the Son (John 3:16–17; 5:37–38; 8:42; 10:36; 17:3, 8; Rom 8:3; Gal 4:4; 1 John 3:10, 14). The word “send” is exapostello, to send out or send forth. It is also used of the sending out of John the Baptist, the angel Gabriel, of sending out the disciples, the sending forth of prophets and the servants in the parable of the wicked husbandmen. No one would argue that these did not exist prior to being sent. If anything, the term implies the commissioning and sending of an existing person suitable for the task. The onus of proof lies with those who would subvert the natural meaning and implication of “sending forth,” to insist that the one sent did not already exist. To argue that the sending of the Son at a given point in time (Gal 4:4) describes the Son’s beginning has no scriptural warrant; it does not prove the Son did not preexist but the Christadelphian interpretation merely presupposes this. But the language of “sending” strongly implies the contrary and does not require the wresting of the preexistence and creation passages to make them “metaphorical.” The Father-Son relationship was already established at the point when, “in the fullness of time,” the sending occurred in the birth from a woman.
This was not a unilateral decision on the Father’s part, however, because there is no conflict or coercion within the Godhead. The Son willingly accepted this foreordained role. It was the role of the Father to send the Son, and the role of the Son to go (John 4:34; 5:30, 43; 6:27; Heb 10:7). The Son, being divine, does whatever his Father does (John 5:17–23) and knows the Father in a unique way (Matt 11:27; John 7:28–29)
Fourthly, the Son, the Father and the Holy Spirit, whilst sharing the same divine essence, are not the same “person” nor are they simply modes or expressions of one being. This was the heresy of the Modalists, who blurred the distinctiveness of Father, Son and Spirit. Christadelphians sometimes seem to confuse Trinitarianism with Modalism when they argue that because the Son is distinct from the Father, he cannot be God. However the Trinitarian position insists that the Son is distinct from the Father and from the Holy Spirit, both ontologically (the way God is in his very being) and in the way God reveals himself to, and interacts with, his creation. This can be seen by the testimony that the Father sent the Son, who willingly went. John Calvin suggests:
To the Father is attributed the beginning of activity, and the fountain and wellspring of all things; to the Son , wisdom, counsel and the ordered disposition of all things; but to Spirit is assigned the power and efficacy of that activity” 
This accords with their complementary distinctiveness in passages such as Ephesians 2:18, 1 Peter 1:2; 1 Corinthians 1:21–22; 12:4–6 and 2 Corinthians 13;14. This is what the doctrine of the Trinity means by three “persons” in one “substance.” We can argue about the precise terminology (as Christians have done for 2000 years) and acknowledge that there might be better vocabulary than “essence” and “person,” were we describing the doctrine from scratch today, but the principles remain the same. In conclusion, the trinitarian position, as against those of Unitarians, Christadelphians and Arians, best accounts for
– the divinity and humanity of the Son
– the preexistence of the Son
– his divine role as creator and worthiness to be worshipped
– his unity with and distinctiveness from the Father
– his divine commissioning and sending and subsequent (re)exaltation.
and we may rejoice that God indeed so loved the world that he sent his Son, not to condemn, but that through him we have eternal life.
1. I have amended this blog since first posted. Originally I stated that “biblical unitarians” might hold an adoptionist position. This was an attempt to distinguish “Christian” Unitarians from “universalist” Unitarians however my choice of terminology was imprecise and too general. According to the website http://www.biblicalunitarian.com/articles/what-do-biblical-unitarians-believe this particular group holds a position which appears similar to Christadelphians (who have owned the term “biblical monotheists” and deny being “Unitarian”). However, other more liberal “Unitarians” have expressed denial of the virgin birth and essentially adoptionist positions. They would most correctly be called Adoptionist to distinguish them from other non-Trinitarians. Other Unitarian websites express a diversity of beliefs which does not necessarily include regarding the Bible as authoritative, despite an acknowledgement of “Judeo-Christian roots” and some can be quite pluralistic, for example https://www.unitarian.org.uk/pages/unitarianism-explained and the Universalist Unitarians.
2.Robert Roberts, Christendom Astray from the Bible (West Beach Sth Aust: Logos Publications, 1984), 160
3. John Calvin, Institutes of the Christian Religion book I ch 13.18, ed. JT McNeill, trans.FL Battles (Louisville: Westminster John Knox, 2006) p 142-3
Further Reading: Julian Clementson, “The Christadelphians and the Doctrine of the Trinity,” Evangelical Quarterly 75/2 (2003) 157–76.