Mat 16:15-16, 21 He said to them, "But who do you say that I am?" Simon Peter answered and said, "You are the Christ, the Son of the living God.".. From that time Jesus began to show to His disciples that He must go to Jerusalem, and suffer many things from the elders and chief priests and scribes, and be killed, and be raised the third day.
It was only after His disciples were able to believe and accept Him as the Messiah the Son of God that our Lord started to show them the gospel of grace with Him, coming as the sacrificial Lamb of God.
Gospel of Jesus
Luke 24:46-47 Then He (Jesus) said to them, "Thus it is written, and thus it was necessary for the Christ to suffer and to rise from the dead the third day, and that repentance and remission of sins should be preached in His name to all nations, beginning at Jerusalem."
The gist of the gospel that our Lord Jesus instructed His disciples to preach:-
1. Jesus was the Christ or Messiah or God was made flesh
2. Jesus suffered
3. He was crucified as the Lamb of God
4. He rose from the dead on the third day, having overcame death, so that Christians can have eternal life with Him.
Gospel of grace to Jews by Peter
Acts 2:22-24, 36 "Men of Israel, hear these words: Jesus of Nazareth, a Man attested by God to you by miracles, wonders, and signs which God did through Him in your midst, as you yourselves also know— Him, being delivered by the determined purpose and foreknowledge of God, you have taken by lawless hands, have crucified, and put to death; whom God raised up, having loosed the pains of death, because it was not possible that He should be held by it... Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ."
On Pentecost Peter preached the gospel of Jesus to the Jews and 3,000 devout Jews repented and became Christians. Later on, Peter preached the same gospel to the Gentiles in Act 10.
Gospel to Gentiles by Peter
Act 10:34, 39-40, 42 Then Peter opened his mouth and said: "In truth I perceive that God shows no partiality... And we are witnesses of all things which He did both in the land of the Jews and in Jerusalem, whom they killed by hanging on a tree. Him God raised up on the third day, and showed Him openly... And He commanded us to preach to the people, and to testify that it is He who was ordained by God to be Judge of the living and the dead.
Gospel of Paul to All
Act 17:2-3 Then Paul, as his custom was, went in to them, and for three Sabbaths reasoned with them from the Scriptures, explaining and demonstrating that the Christ had to suffer and rise again from the dead, and saying, "This Jesus whom I preach to you is the Christ."
Paul preached the same gospel as Peter to both Jews and Gentiles.
Acts 17:16-17 Now while Paul waited for them at Athens, his spirit was provoked within him when he saw that the city was given over to idols. Therefore he reasoned in the synagogue with the Jews and with the Gentile worshipers, and in the marketplace daily with those who happened to be there.
Same Gospel of Grace to All
Eph 3:5-6 which in other ages was not made known to the sons of men, as it has now been revealed by the Spirit to His holy apostles and prophets; that the Gentiles should be fellow heirs, of the same body, and partakers of His promise in Christ through the gospel,
God gave to the Apostles the same gospel of grace for both Jews and Gentiles.