He committed no sin, neither was deceit found in his mouth (1 Peter 2:22).
The New Testament insists that Jesus was entirely free from sin (John 8:46; 2 Cor. 5:21; Heb. 4:15; 7:26; 1 Pet. 2:22; 1 John 3:5). This means not only that he never disobeyed his Father but that he loved God’s law and found wholehearted joy in keeping it. In fallen human beings, there is always some reluctance to obey God, and sometimes resentment amounting to hatred at the claims he makes on us (Rom. 8:7). But Jesus’ moral nature was unfallen, as was Adam’s prior to his sin, and in Jesus there was no prior inclination away from God for Satan to play on, as there is in us. Jesus loved his Father and his Father’s will with all his heart, mind, soul, and strength.
Hebrews 4:15 says that Jesus was “tempted in every way, just as we are,” though without sinning. This means that every type of temptation that we face—temptations to wrongfully indulge natural desires of body and mind, to evade moral and spiritual issues, to cut moral corners and take easy ways out, to be less than fully loving and sympathetic and creatively kind to others, to become self-protective and self-pitying, and so on—came upon him, but he yielded to none of them. Overwhelming opposition did not overwhelm him, and through the agony of Gethsemane and the cross he fought temptation and resisted sin to the point where his blood was shed. Christians must learn from him to do likewise (Heb. 12:3-13; Luke 14:25-33).
Jesus’ sinlessness was necessary for our salvation. Had he not been “a lamb without blemish or defect” his blood would not have been “precious” (1 Pet. 1:19). He would have needed a savior himself, and his death would not have redeemed us. His active obedience (perfect lifelong conformity to God’s law for mankind, and to his revealed will for the Messiah) qualified Jesus to become our Savior by dying for us on the cross. Jesus’ passive obedience (enduring the penalty of God’s broken law as our sinless substitute) crowned his active obedience to secure the pardon and acceptance of those who put their faith in him (Rom. 5:18-19; 2 Cor. 5:18-21; Phil. 2:8; Heb. 10:5-10).
Adapted from Concise Theology: A Guide to Historic Christian Beliefs by J.I. Packer