We are not to deny ourselves assurance until we have reached perfection. The Christian is a sinner who is in the process of being transformed, and his assurance is that God has called him, not that he has already reached his goal.
Why doesn’t John reason here as he did in verse 20? Why doesn’t he say, 'If our heart condemn us not, God is greater than our hearts and knows all things’, for this obviously remains true? Even though our hearts do not condemn us, it would be easy for God to find fault with us if he wished to. But he is the God of peace and he wants us to have peace even though we still have residual sin. Conscience may fail to spot sin in us, and yet God wants us to heed its approval when we obey, just as much as he wants us to heed its condemnation when we sin. We are not to be over-scrupulous and constantly saying, ‘Though I am not aware of it, there must be much sin in me and I must therefore force myself to feel guilty. Only then am I seeing myself accurately.' This is to try to improve on God’s testimony in our hearts. It may be true that there are sins that we are unaware of, but we will be led to deal with these as part of tomorrow's lesson. Today our heart does not condemn us and we should have assurance towards God.