5Now I ask you, lady, not as though I were writing to you a new commandment, but the one which we have had from the beginning, that we love one another.
6And this is love, that we walk according to His commandments This is the commandment, just as you have heard from the beginning, that you should walk in it.
John explains what it means for us to love God. It seems to be a reciprocal event. As we follow His commandment to love, we are simultaneously loving Him. I find this to be one of the truths of God that is ironic. (similar to being blessed as you tithe with a tax deduction).
As a reminder, we should remember that this is something we get to do, and in doing so, we are blessed abundantly. It’s about putting yourself in a place of blessing. For God is love and without receiving His love we are incapable of loving others the way He loves us. As I’ve mentioned before, following God’s will is something He will not force us to do, therefore leaving it up to us to decide. The 5 elements I mentioned in the previous passage are the things we receive as a result of following His commandments (aka His will).
I also like how John specifies that he is not telling them anything new, simply reminding and encouraging the reader. This is especially key since the next section of his letter discusses false teachers (seems to be another reoccurring theme in the new Testament)