“And by this we know that we are of the truth, and shall assure our hearts before Him.”
The place where we need assurance is “before Him”. We do everything in the presence of the Lord. “Before Him” expresses God’s pleasure and will. God knows the worst in us yet He still desires our fellowship. The Greek implies that we will meet the Lord face to face. This is the believer in fellowship, living in the Spirit-filled life. He knows with assurance that he walks with the Lord.
Conviction and certainty come from what the Lord gives us, not what we do for ourselves.
A Christian who understands the grace principle knows that he does not have to make restitution for his sins. He knows that he does not have to pay with a subjective guilt for his sins, that is, punish himself for his sins.
This Christian understands that Jesus took all the punishment and penalty for his sins. He knows that taking a vow to never do it again is error. He knows that he does not have to attend the evening service for a year to make up for his sins. His confidence is in the Lord, not in himself.