"By this we know that we love the children of God, when we love God, and keep his commandments."
1 John 5:2
This is interesting. I think I was expecting the opposite... that we prove our love for God by loving his children. And, in fact, there are scriptures that suggest that as well (1 John 4:7 or 4:20 for instance). So, the whole thing is kind of circular. Loving God helps us to love others. And loving others helps us to love God. Loving God might be the right place to start, as Christ said it was the first and great commandment (Matthew 22:38), but loving others is the second, and they can't really be separated from each other, since they work together.
Even though it is easy to think that we can love one person and hate another, and keep those totally separate, hate bleeds into everything else. We can't love God unreservedly when we hate someone else... and we can't love someone else unreservedly when we hate God. Parts of ourselves are still swallowed up in the hate. Hate hurts us; it poisons who we are.
The verse mentions keeping God's commandments as well, and at first we might think... why? What do rules have to do with love? But the cool thing about God, and his rules, is that all of it is designed to teach us love. Everything God does is designed to bring us all together in unity, truly caring for and helping each other to be happy. Today, let's show our love for others by loving God, and keeping his commandments. And that, in turn, will enlarge our capacity to love others, and God, and so on, as we get closer to Zion and perfect love.