(Esther 2:11) "And every day Mordechai would walk in the courtyard of the harem, etc.": He said: Is it conceivable that this righteous one (Esther) is to marry this uncircumcised one (Achashverosh)! It must be that something (momentous) is in store for the Jews, and that they are destined to be redeemed through her.
Like David, He Recognized It Immediately
Mekhilta Tractate Amalek 2:35