sorry if i am being annoying wht is the point of Qe3
Bb6, of course.
It does have the tactical drawback of 18.Qe3 Nc4, when the queen is attacked, and white has to take the knight immediately.
18.Qf2? does not have this drawback, but falls into Gelfand's nasty sacrifice 18...Rc6! 19.f4 Rfc8!
The threat is trapping the queen, and forces the exchange of black's best peice bg7.