Prevents b5 and the pushing of the bishop back. However, the knight at c6 is now free to move to b4 without the a2 pawn being able to force it back.

Strange move. I stand to gain a pawn.

Using the knight at c3 to capture the d5 pawn would have prevented this move by black.

A more dangerous move then may appear at first glance thanks to the pawn at c5. The knight is threatening both the bishop at d5 and the pawn at c2. If I move the bishop to b3, c4 will cost me a rook. If I move the bishop to e4, f5 will force it to d3. Then, c4 will once again cost me a rook.

Either my bishop or rook is doomed. I decide to sacrifice the bishop but capture a pawn and ruin black's castling in the process.

I have to ruin my castling options to prevent knight to c2.

More pressure on the c2 pawn.

Strange move. Black didn't have to retreat.

Trying to build a defense by preventing c4.

Black also seems to be in defensive mode.