The Apostle uses the word "coming" to signify this idea of communion because he later uses the image of the priesthood. In the Old Testament the priests serving in the temple are called those who come, or draw near, to God (Lev 16:1; Num 9:13; Ezek 40:46).
In the New Testament, through Christ, access to God has been opened to all believers (Heb 9:1 and following; Heb 7:25; Heb 10:22; Heb 10:6; Heb 4:16).
Although by regeneration itself the Christian has been placed, and stands, in communion with Christ, this not only does not remove the need for constant and ever fuller communion with Him. On the contrary, it contains that necessity within itself.
For this reason the word "coming" is used, in the sense of an unceasing striving to draw near to Christ.
"A living stone": the Apostle later cites Isaiah's prophecy about the cornerstone which Jehovah God will lay in Zion as the foundation of a new building (Isa 28:16; cf. Ps 117:22).
Christ Himself refers this prophecy to Himself, understanding the stone as Himself (cf. Mt 21:42 and note). The Apostles interpret it in this sense as well (cf. Rom 9:33), and Peter himself does so in his speech before the Sanhedrin (Acts 4:11) and here.
According to the meaning of this figurative depiction, the Christian community is the house, or temple, of God. The individual members of this community, that is, each Christian, are the stones from which this temple is built.
Christ is the cornerstone on which the whole building rests. See the notes on Mt 21:42 and Acts 4:10.
He is called a living stone in the same sense in which Christ calls Himself the living bread (Jn 6:51; cf. note and parallels). Namely, He has life in Himself and is the source of life for all that lives.
In particular, He is the source of life for those who believe in Him (Jn 1:4; Jn 5:28; Jn 6:68; Jn 14:19 and following; Jn 4:10; Acts 2:28; cf. the notes on all these passages).
He penetrates and fills with His life and life-giving power the whole body of His Church, which grows through Him.
"Rejected by men, but chosen by God": Ps 117:22. In the Psalmic image, and likewise in Christ's interpretation of it (Mt 21:42) and in the Apostle Peter's own interpretation (Acts 4:11), this is said only of the builders of the building.
They rejected this stone as unsuitable for construction. Here it is applied to all people, to the whole sinful and darkened world, in contrast to God, who is holy and most wise.
The concept is generalized for a sharper contrast, as in Jn 1:10-11; see note. Believers in Christ are presented as an exception from this sinful world that rejected Him.
But this false judgment of men about the stone is opposed by the unerring judgment of God about it. According to that judgment, this stone is chosen, in the sense of being the best of all, and precious in the sight of God.
It alone is the stone upon which the temple of God can be built without fear of its collapse. It alone can be the cornerstone, firmly bearing the whole building upon itself.
Christ, rejected by the unbelieving world, is the foundation of the Church, which saves believers from eternal destruction.