"love his brother" - 1 John 4:21
In "Biblical Perspective" for this lesson, Dr. Gordon Snider writes:

Lest we think that love is the easy way out, John had a word of warning. If a man say, I love God, and hateth his brother, he is a liar. If my love for God is not seen in my love for others, I don’t love God. It is that simple. It is easy to say that we love God, but do our actions toward others prove it? Love is to be the top priority in every relationship.

Source: "Biblical Perspective", Adult Teacher's Insights, page 7.