You would only call on someone to save you if you believed they were able to do it. That’s Peter’s point. God has made a way for us to be saved. Jesus is the Christ; He came from God, was ordained by God, took the punishment our sin deserved, was raised by God to life, “death has no more dominion over Him”. When you realize that you are drowning in your own sin, destined to die with no way out, if you believe that Jesus is mighty enough to save you, then call on His name. Everyone who calls upon the name of the Lord shall be saved.