How to block check from opposing queen

Hi, I'm relatively new to chess. 

I was analysing my game when I learned that blocking a check from the opposing queen using the knight is better than a bishop.

Why is this the case?

Thanks in advance

Your move was not great but worked.  Nc3 is likely better.

Perhaps because the resulting position allows black to get the bishop pair and weaken the b2 pawn? Just a guess from an intermediate player, but as a general rule the game analysis should help answer those questions. Just follow the line of best engine moves from your innacuracy, and it will often reveal why it was inaccurate.

Bd2 seems to allow the Black queen to go to Qb6 which attacks the b2 pawn then once white defends b2 pawn it starts a focused attack against the d4 pawn with Nc6 and e5.

That's exactly what my opponent did, actually.

His moves were Qb6 then Qb2 ( I did nothing to defend my pawn, unfortunately) and I had no option to save my rook. 

Thanks for the insight !!

Chances are if your opening is decent you won't end up in that position to begin with.

From the basic material chess point of view Bd2 wasn't a mistake but after Qb6 with the attack on the b2 pawn you would have to play b3,Bc3 or even go back with Bc1 and then the focused attack on d4 would be considered higher material chess which would be hard to see in fast games.