John Calvin: Keeping God’s Commandments and Certainty of Faith

And by this we know that we have come to know him, if we keep his
commandments. (1 John 2:3)

But there is no one who in everything keeps them; there would thus be no knowledge of God in the world. To this I answer, that the Apostle is by no means inconsistent with himself. Since he has before shewed that all are guilty before God, he does not understand that those who keep his commandments wholly satisfy the law (no such example can be found in the world); but that they are such as strive, according to the capacity of human infirmity, to form their life in conformity to the will of God. For whenever Scripture speaks of the righteousness of the faithful, it does not exclude the remission of sins, but on the contrary, begins with it.  

But we are not hence to conclude that faith rests on works; for though every one receives a testimony to his faith from his works, yet it does not follow that it is founded on them, since they are added as an evidence. Then the certainty of faith depends on the grace of Christ alone; but piety and holiness of life distinguish true faith from that knowledge of God which is fictitious and dead; for the truth is, that those who are in Christ, as Paul says, have put off the old man. (Colossians 3:9.)

John Calvin’s Commentary of 1 John

Emphasis added