What does 1 John 3:21 mean?

When we have a clear conscience, we can have great confidence before God. Our confidence in His love is unconditional, and for all people (John 3:16), regardless of what we do. But the confidence we have in God's approval is conditional. We must be in fellowship with God—we must "abide in" Him—before we can have confidence in that aspect of our relationship with Him. God will only "approve" those things which are according to His will (Romans 2:7–11). Based on the information John has given so far in this letter, we can gauge whether or not we are living according to the will of God. And, when we realize we've fallen short, we can rest in God's knowledge and forgiveness (1 John 2:1).

John emphasizes confidence in other places in this letter. In 1 John 2:8, he wants believers to seek reasons for confidence, instead of shame. In 1 John 4:17, John notes that the work of God's love in us gives us confidence under His judgment. Likewise, we can have confidence that God hears our prayers (1 John 5:14). A close walk with God leads to a humble confidence, which leads to bold prayer and looking forward to the return of Christ.