As those who have proactively put off the old and put on the new (3:9b-10), we are now called to exhibit the new traits that belong to God's chosen people.
God's Chosen People (12a): So far, Paul has emphasized our active role in our repentance and conversion.[1] This doesn't, however, mean we chose God. Instead, God chose us. Thus, we are called "chosen of God."[2] Moreover, we are objects of God's love ("beloved")[3], and we are set apart ("holy") unto God.[4] All of this privilege means a duty to live up to our identity as God's chosen people.
New Traits (12b-14): Hence, Paul calls us to put on the new traits that befit God's people: compassion,[5] kindness, humility, gentleness and patience. He then brings up two actions we are to maintain: forbearance ("bearing with one another") and forgiveness ("forgiving each other").[6] With the latter, we are to reflect the Lord's treatment of us.[7] Lastly, we are to put on love like a coat that covers everything underneath.[8] Paul also specifies that this is the love believers already know to practice.[9] This is also the glue ("perfect bond") that holds the church together, and without it, the church falls apart.
[1] Paul repeatedly used the middle voice in 3:5-10: "put to death," "put aside," "put off," and "put on."
[2] Or, "elect of God" (NKJV). Scripture often describes believers as this (cf. Rom. 8:33; Eph. 1:4; 1 Pet. 1:1-2).
[3] "Beloved" is a passive participle (ē-ga-pē-men-oi [ἠγαπημένοι]). We are here seen as recipients of God's love.
[4] We are set apart unto God. Cf. 1:22 ("holy before God"); 1:26 ("His holy ones"); 2 Cor. 6:17-7:1; 1 Pet. 2:5.
[5] NASB's "heart of compassion" is literally "bowels of compassion." This is affectionate mercy toward others.
[6] "Bear with" is the opposite of passion (as in anger and wrath). The second verb "forgive" comes from the noun "grace [cha-ris (χάρις)]," and it emphasizes the gracious treatment of others. These are both set in contrast to the earlier vices (3:5, 8). Lastly, both verbs are imperfective, hence, continual. We keep these up.
[7] Scripture resounds with the call to imitate God's forgiveness toward us (cf. Matt. 18:32-35; Eph. 4:32).
[8] "Beyond" is literally "upon," so that love is seen as overarching the other traits. This imagery continues the clothing metaphor. The primacy of love is repeated throughout Scripture (cf. 1 Cor. 16:14; 1 Pet. 4:8).
[9] "Love" is articular and points to their love, which Paul had heard about (1:4, 8). Cf. also 1 Thess. 4:9.