in compared with into
Into is something going from the outside into the inside.
In is something innate inside us, as my stomach is in me.
Now food goes into my stomach. We might say, "The food is going in my stomach" by convention, but in reality it is going into my stomach.
I jump INTO the lake. Once that happens, then I am IN the lake. There is a difference.
The baptism of repentance into the forgiveness of sins (). This is what the Greek says. The English has it as "preach the baptism of repentance for the remission of sins." It is a baptism of repentance, and repentance for the forgiveness of sins. It is not a baptism for the forgiveness of sins. This is a baptism of repentance, that is, the people have repented, are showing they already have repented, and so are baptized by John. So then, ...repentance into the remission of sins. This means that the remission of sins is not something innate in us but rather goes into us by our repentance. The baptism is a testimony that we have repented.