Peter was proclaiming Jesus' deity as well as the fact that He is Israel's promised Messiah. Dr. Stanley D. Toussaint, Senior Professor Emeritus of Bible Exposition at Dallas Theological Seminary, writes the following comments on Acts 2:36:

"Here is the conclusion to Peter's sermon. The noun 'Lord', referring to 'Christ', probably is a reference to Yahweh. The same word 'kyrios' is used of 'God' in verses 21, 34, and 39 (cf. Phil. 2:9). This is a strong affirmation of Christ's deity " (Walvoord & Zuck, The Bible Knowledge Commentary; New Testament [ChariotVictor Publishing, 1983], p.359).

The Jews who believed that Jesus is Christ, God come in the flesh, were "born of God". Dr. Zane Hodges, past Chairman of of the New Testament Department at Dallas Theological Seminary, writes the following in regard to Peter's words:

"Peter concludes his address with the assertion that 'God has made this Jesus, whom you have crucified, both Lord and Christ' (2:36). His hearers then reply, 'Men and brethren, what shall we do?' (2:37). But such a reaction presumes their acceptance of Peter's claim that they have crucified the one who is Lord and Christ. If this is what they now believe, then they were already regenerated on Johannine terms, since John wrote: 'Whoever believes that Jesus is the Christ is born of God' (1 John 5:1; cf. John 20:31) " [emphasis added] (Hodges, The Gospel Under Siege, p.101).

Here are the verses to which Hodges makes reference: "Whosoever believeth that Jesus is the Christ is born of God...Who is he that overcometh the world, but he that believeth that Jesus is the Son of God? " (1 Jn. 5:1,5).

This clearly shows that the "gospel" by which the Jews were "born of God" was a gospel that speaks of His "identity," that He is Christ, the Son of God:

"But as many as received Him, to them gave he power to become the children of God, even to them that believe on His Name: Who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God " (Jn.1:12-13).

As already demonstrated, the "gospel" that Paul preached to the Gentiles was the "gospel of grace," and it is this gospel whereby the sinner is "begotten" today, as witnessed by Paul's words here:

"For though ye have ten thousand instructers in Christ, yet have ye not many fathers: for in Christ Jesus I have begotten you through the gospel. Wherefore I beseech you, be ye followers of me" (1 Cor.4:15-16).

Today we are to follow Paul and preach the "gospel of grace" and all who believe this gospel are born of God. On the Day of Pentecost the believers were born of God when they believed that it is Jesus Who is the Christ, the Son of God.