Since God is kind, and since He commands us to be kind (Ep 4:32), we ought to understand what kindness is.
Kind is not nice, avoiding conflict, difficulty or discomfort; at times we’re called to speak the truth (Ep 4:15) even when it wounds. (Pr 27:6) Nice is generally selfish and fearful; seeking approval and acceptance; this isn’t the servant of Christ. (Ga 1:10)
Kindness isn’t passive, weak, insecure or timid; God commands us to be strong (1Co 16:13); Kindness can be bold (Pr 28:1), standing firm (Ep 6:13), confronting evil and defending ourselves as needed. (Lk 22:36)
The root words from which we get our English word kind also give us our word kin; as if God’s calling us to treat one another like family: we are all related, members one of another. (Ep 4:25) The Greek is chrestos or useful, suggesting moral helpfulness and benevolence, also translated easy (Mt 11:30), good (Ro 2:4), and gracious. (1Pe 2:3) It’s how we treat our loved ones.
Kindness is love in action (Tit 3:4), loving my neighbor as myself, seeking their ultimate welfare. Love persists in kindness (1Co 13:4), for love perfects and completes kindness. (2Pe 1:7)
The opposite of kindness is evidently malice (Ep 4:31): having ill will, animosity, wanting less than the best for another. This is often rooted in vengeance, thinking others deserve less than the best, rendering our own sense of justice rather than letting God do so. This is, at it’s root, unbelief in the goodness of God (Ro 2:2), refusing to walk in love and let God be God.
If God is ever inviting us to what is best, both for ourselves and others, if He is never malicious, then we should be like Him. (Lk 6:35) This is our design, when we’re at our best and bring Him glory, being like Him, full of grace and truth. (Jn 1:17)