1.d4 d5
2.c4 c6
3.Nf3 Nf6
3.e3 e6
4.Nc3 Nbd7
5.Bd3 dc4
6.Bxc4 b5

now what's the different between 7.Bd3 and 7.Be2  in accordance with incoming Black's Bb7,b4 and so on.

one thing i notice is that in 7.Be2 var,  later after Black's b5-b4 pawn push, white's knight will go to a4.  in 7.Bd3 var, knight can go to a4 or e4,  but mostly to e4.

what's the main idea between those two ? i think 7.Be2 has it's pro and cons. any opinion is appreciated.

thanks in advance