Do you know the reason that Jesus shed His blood? Of course, you do. What if someone tried to convince you that Jesus shed His blood “because sins had already been forgiven”? Would that make sense to you? No! You know that Jesus shed His blood “for” (i.e., in order that) “the remission of sins” might be obtained (Matt. 26:28).
That same terminology is used in a command to mankind in Acts 2:38. Whatever the expression meant in Matthew 26:28 is what it must mean in Acts 2:38. Peter said, “Repent and baptized for the remission of sins.” Some have tried to argue that “for” means “because sins have already been forgiven.” It cannot mean that in this verse any more than it would mean that in Matthew 26:28.
Jesus shed His blood in order that forgiveness of sins might be obtained, and sinners must repent and be baptized in order that forgiveness of sins might be obtained. The meaning of that expression is identical in these verses, which ties the blood of Jesus to the essentiality of baptism to be forgiven of sins.