This is how we know that we know him: if we keep his commandments.

 This is an approach which Paul continually uses. He writes to the Thessalonians: "But concerning love of the brethren you have no need to have any one write to you, for you yourselves have been taught by God to love one another" ( 1 Thessalonians 4:9). What they need is not new truth but to put into practice the truth they already know. He writes to the Romans: "I myself, am satisfied about you, my brethren, that you yourselves are full of goodness, filled with all knowledge, and able to instruct one another. But on some points I have written to you very boldly by way of reminder, because of the grace given me by God" ( Romans 15:14-15). What they need is not so much to be taught as to be reminded. 