Yevamos 117a #1: Hate is reciprocal. (A woman's step-daughter, and her mother-in-law, are not believed to testify that her husband died ¹ , for they have reasons to hate them. Therefore, a step-mother and a daughter-in-law are not believed.)

Yevamos 117a #2: Understanding in Torah is according to one's effort (alternatively - how well his Rebbi explains things).

Rashi: The face that you show to water, it shows you such a face (a reflection). So one who knows that his colleague loves him, so he shows a face to him.

Orchos Tzadikim (Sha'ar ha'Zechirah): One who smiles at you, you should remember how much his heart leans to love you [and you should love him].

Malbim: The heart sends blood to all limbs, and gives life to all of them. All limbs return the choice blood to the heart. It turns out that the heart returns to man what it received from him. It is like water - one who looks at it sees his face. The water returns the same face that it receives from the man standing opposite it. The heart "u'Magid l'Adam Mah Sicho" (Amos 4:13). All powers of man, their form is seen in the heart. It sees all his powers, and prophesizes for him good or bad.

Malbim (Nimshal): The Kelali heart of the Kelali body - the king is the heart of the country, the Chacham is the heart of the congregation. The taxes that they give to the king, they return and receive it, just like the limbs receive [blood] from the heart that they influenced to it. Similarly, what people give to support a Chacham, they receive influence in his merit. Hashem is the heart of the creation. According to how they prepare their deeds, Gevurah of above will influence Brachah on them. Tziyon is the heart of Eretz Yisrael. The influence that they brought to Tziyon and the Beis ha'Mikdash returns to the nation - "Ki Sham Tzivah Hashem Es ha'Brachah" (Tehilim 133:3).