Kindness is the trait of treating others with warmth and consideration, in word and deed. It shows in small things: how we answer a tired colleague, how we speak about someone who is absent, whether we notice who needs help. Kind people are often easier to trust, and their kindness tends to spread. The Gita treats kindness as part of wisdom and not as softness.
Gita 6.32 describes the highest yogi as one who regards the happiness and suffering of others as no different from his own, so before speaking or acting, consider how you would feel in the other person's situation. Gita 12.13 portrays a devotee with no hatred who treats all beings with friendship and compassion, and Gita 16.2 lists harmlessness, truthfulness, gentleness and compassion among divine wealth. Gita 17.15 says words should be truthful, agreeable and helpful, and never hurtful.
The Gita also shows gentleness and its limits. Gita 11.50 shows the Lord returning to a gentle form to console Arjuna after revealing overwhelming majesty, so be gentle yourself with those who are overwhelmed. Gita 1.35 shows Arjuna's compassion not yet joined with clear understanding of duty, so let compassion guide your conduct but join it with wisdom. Gita 16.19 treats habitual cruelty and hatred as serious obstacles, so replace them with patience, fairness and consideration. Gita 1.27 and 1.37 note how painful conflicts within families are.