Would someone explain this to me?

Would anyone here care to explain this game sequence to a relatively weak player? Am I overlooking something obvious? Why is Be4 (which prevents my opponent's knight from forking my rooks) a mistake while Nxb6 is the 'best' move?

When I checked another engine, it says f3 for white is the best move. The idea is that after Nf2 forking the rooks, you play Nc7 and the knight become safe. Your knight is strong since it is in the opponent side, and after Nc7, and your opponent takes one of the rooks (Suppose he take h1 rook. The knight will just be useless there and soon to be captured. And if he takes the other rook, the knight will just be captured too.) Also, after you played that move (Be3), your opponent will take your knight (3 points) let’s say it is -3 points for you. But after f3 Nf2, Nc7 Nxh1 . You will be here -5 points. But you will soon capture the knight, so we can say you are here -2 points. Also, the knight in a8 is really strong, so we can say -1 points. So I hope you get it. The f3 sequence lead to better position, and Be3 lead to worser position. It is not like I am good at teaching, but felt bad that this was September comment, and no one replied. I won’t be upset if you didn’t even understand what I am saying.

Agreed, sorry no one offered a response before now.  Hope this helps:

12. Nxb6 is the superior move because of 13.Rd7+ & 14.RxBb7 (black’s B is hanging); if Black is careless and chases the rook fork, Black loses more material. 12….axb6 is forced
13. Nh3 eliminates the rook fork threat; 13….e5 threatens Bishop
14. Re1 threatens RxN+ if exBf4; 14….g6 prepares Bg7, developing & opening back rank for rook
15. Bd3 attacks unsupported Ne4; 15….Nd6 is forced
16. Bxe5 threatens 17.BxRh8 & discovered check; 16….NxBe5 is forced
17. RxNe5+

Additional comments for this line of play:

• White’s two concerns (Na8 capture) & Nxf2 forking rooks are resolved favorably in two moves
• Allowing BxNa8 without resistance in this position only helps Black equalize in material
• Defending Nxf2 before addressing Na8 helps Black as White loses its advantage
• Nh3 is better than Be3 to counter the rook fork as it develops a piece and opens back rank to connect rooks after Bd3
• White is “fully developed” at move 15; Black will take several moves longer
• After move 11, White is +4 material points, at 17, +3; advantage maintained
• After move 15, Black has retreated to its half; White is pressing the initiative
• Black moves are “forced”, allowing White to gain tempi
• White’s position is solid after move 16, and can gain control of the center files

Regards