Where Jude previously affirmed that God’s church is kept for Jesus Christ, here he turns the indicative (statement) into an imperative (command)—they must keep themselves in the love of God. In the New Testament, to keep
can mean to obey God’s law (1 Timothy 6:14; James 2:10; 1 John 2:3–5; 1 John 3:22, 1 John 3:24; 1 John 5:3; Revelation 12:17; Revelation 14:12), or to hold onto something such as unity (Ephesians 4:3) or faith (2 Timothy 4:7), or even to maintain a certain state such as purity (1 Timothy 5:22; James 1:27). In this context, to keep yourself in the love of God is to flee apostasy. Practically this means building yourself up in the faith (Jude 1:20), praying in the Spirit (Jude 1:20), and waiting for the mercy of Jesus Christ (Jude 1:21).1
21 keep yourselves in the love of God, waiting for the mercy of our Lord Jesus Christ that leads to eternal life.