Rashi: [One with a pure heart loves] one whose lips are grace.

R. Yonah: Tehar Lev is one whose love is clear and pure. This love does not depend on a [physical] matter. He does not love only for his own pleasure. However, he loves his friend because he did much good for him. He is obligated to love him even if he does not hope to get more good from him. Or, he loves him due to his attributes. Everyone must love those who fear Elokim and are Anshei Emes. His love should be faithful, to toil for his benefit and to help him and alleviate his pain. He does not do so for reward; it is an obligation of love. His lips are grace in front of his beloved. In all his words and counsel, his pure love is recognized. Regarding a hater, it says "bi'Sefasav Yinacher Sonei" (26:24). When there are roots in the hearts, the branches are seen on the tongue. He will show love only from a full heart.

Malbim: After commanding to expel the Letz, who arouses quarrels, and not to mingle with him, now it says oppositely. One who loves everyone, he has a pure heart and his lips are grace - the opposite of a Letz, whose heart is full of dross and his lips are full of quarrels. He hates everyone. A faithful lover, his heart and mouth are the same. He does not speak mockery, only words of grace.

Rashi: Hashem loves and endears him.

R. Yonah: He is proper that the king be his friend. The king must search for people whose love is clear and pure; there are few such people - "Adam Echad me'Elef Matzasi" (Koheles 7:28). This Midah is found only in a straight person. Amidst love of straightness, he loves one whom we are obligated to love. He strives to fix him, without intent to get reward or honor from the good that he does. The coming verse proves so. It was proper to put our verse next to "Tov Ayin Hu Yevorach" (9). It interrupted with "Garesh Letz v'Yetzei Madon" (10), for first one must separate from bad company, and afterwards seek good company.

Malbim: It is proper that even the king be his friend.