3:19-20 "By this"refers to what John said in verses 17-18. Tangible demonstrations of love for the brethren show the believer's true character. They should be a comfort to us when we feel guilty that we have not met many needs, a condition that prevails no matter how generous we may be. We can overcome feelings of false guilt by remembering that God knows our real motives. He does not judge on the basis of appearance as we often judge ourselves.
"This phrase ["before Him,"v. 19] could refer to standing in the presence of God on the day of judgment (4:17), an occasion which might well fill the heart of a man with foreboding. But the context here is one of prayer: dare we approach God with our requests if we feel guilty before him? On the whole, it seems more likely that this is what is in John's mind (cf. 1 Thess. 1:3; 3:9). We then have a smooth transition to verse 21.
"To be sure, the occasion can be generalized. What John says can be extended to any and every occasion when the believer is in doubt about his situation before God."136
"We shall then still our heart in whatsoever it may condemn us, because we are in fellowship with God, and that fact assures us of His sovereign mercy."137
3:21-22 True love for the brethren demonstrated in deeds of self-sacrifice enables the believer to face Jesus Christ unashamedly whenever He may appear (cf. 2:28). John stressed the importance of a clear conscience again (cf. 1:7; 2:2; Heb. 9:9, 14; 10:2, 22; 1 Tim. 1:19). Shamelessness can give us appropriate boldness to approach God's throne of grace in prayer even now (cf. John 8:28-29). We will receive our requests if such is the will of God. John did not state this condition here, but he mentioned it later (5:14-15).
"There is nothing mechanical or magical about prayer. For it to be effective, the will of the intercessor needs to be in line with the will of God; and such a conformity of wills is brought about only as the believer lives in Christ."138
"Obedience is the first condition for answered prayer, when that prayer is offered by a child of God. The second, related condition is willing service: the determination to do' always (poioumen, present) what pleases God."139
