19 Repent therefore and be converted, that your sins may be blotted out, so that times of refreshing may come from the presence of the Lord,
The nation of Israel turned away from God by rejecting their Messiah, Jesus. This verse is a call to embrace Him as their Savior.
19 Repent [change your mind]
Peter’s challenge to Israel was that they were to “repent” of their rejection of Jesus as the Messiah. The word “repent” does not mean to feel sorrow for sin. It carries the idea of a change of mind or turning from one viewpoint to another. The Jews needed to change their minds about Christ, their Messiah and Savior. Genuine faith involves repentance about something. In the case of Acts 20:21, it involves repentance toward God and faith in our Lord Jesus Christ.
The “therefore” here carries the idea of then. What Peter argued from this point rests on the previous part of his sermon. Since God glorified Jesus as the Messiah, it was necessary for the nation Israel to repent and be converted.
and be converted,
The word “converted” means to turn about. The idea is to turn from rejecting Christ as the Messiah to embracing Him as the Father’s Sent One. Conversion is evidence of repentance.
that your sins may be blotted out,
The purpose clause beginning with “that” points to a near event to individual hearers of Peter’s sermon. Individuals listening to Peter’s sermon would have their sins “blotted out” or completely wiped out at the point they embraced Jesus as the Messiah. When God forgives, He wipes the penalty clean; He will never hold the person responsible for what they did again.
God’s forgiveness is decisive.
When God forgives, He wipes the slate clean. The challenge to convert to Christianity here is for individual Jews, not for the nation Israel. The only way God offers forgiveness is through trust in what Christ did on the Cross (Acts 10:43; Eph 1:7).