Another reflection on mission and the Trinity (and perhaps an example of how biblical studies could lead into systematic theology).
When Jesus was baptized and went up from water, a voice from heaven said, “This is my beloved Son, with whom I am well pleased.” The voice is a conflation of Psa 2.7, “The LORD said to me, ‘You are my Son; today I have begotten you'”, and Isa 42.1, “Behold my servant, whom I uphold, my chosen, in whom my soul delights.” Both of them were read messianically in that era, and hence the voice served to confirm messianic calling of Jesus.
On the word ‘son’ itself, it was initially applied to Israel when YHWH told Moses to tell Pharaoh to let Israel go from Egypt: “Israel is my firstborn son, and I say to you, ‘Let my son go that he may serve me.’ If you refuse to let him go, behold, I will kill your firstborn son.” (Exo 4.22-23) The interplay is of course between YHWH’s son and Pharaoh’s son.
Then the word was used to denote the Messiah, since the Messiah is the representative of Israel, as indicated earlier in Psa 2.7. If Israel is YHWH’s firstborn son, the Messiah, the representative of the son, could bear the title of ‘son’ as well. The Messiah is son of YHWH.
The Messiah, on the other hand, literally means ‘the anointed one.’ Anointment in the Ancient Israel was done for high-profile public officers, like king or priest, e.g., Saul (1 Sam 9.16) and David (1 Sam 16.13) who were anointed by Samuel. They were anointed with oil and from that day forward the Spirit of YHWH was upon them (for Saul’s case, until David was anointed, signifying change in kingship). The oil symbolized the Spirit and the blessing of kingship. And Jesus was anointed as well by the Spirit: “He saw the Spirit of God descending like a dove and coming to rest on him.” (Mat 3.16)
Indeed, the Isa 42.1 itself indicated that the Servant whom YHWH delights would have the Spirit of YHWH to rest upon him: “Behold my servant, whom I upload, my chosen, in whom my soul delights; I have put my Spirit upon him; he will bring justice to the nations.” (Isa 42.1)
So in overall this scene after the baptism of Jesus signified the anointment of Jesus. Jesus was now the Servant King of Israel. From that day forward Jesus started his public ministry under the guidance of the Spirit. Like David, when he was anointed, he was not enthroned yet. David would be enthroned much later after he was anointed. And Jesus would be enthroned on the cross. To sum up, the scene signified how Jesus was sent by the Father to do his mission under the guidance of the Spirit. And that’s the Trinity in a nutshell.
What about the church, then? I have argued earlier that the mission of the Son is paradigmatic for the church. And, since the mission of the Son is trinitarian, the mission of the church is trinitarian as well. The people of God was sent by the Father as an extension of the Son under the guidance of the Spirit. And that’s the trinitarian character of the mission of the church. As Jesus himself put it on the Gospel of John, “As the Father has sent me, even so I am sending you… receive the Holy Spirit.” (Joh 20.21-22)