Matthew 22:34-40 1 John 4:20-21

34 But when the Pharisees heard that He had silenced the Sadducees, they gathered together. 35 Then one of them, a lawyer, asked Him a question, testing Him, and saying, 36 “Teacher, which is the great commandment in the law?” 37 Jesus said to him, “ ‘You shall love the LORD your God with all your heart, with all your soul, and with all your mind.’[d] 38 This is the first and great commandment. 39 And the second is like it: ‘You shall love your neighbor as yourself.’[e] 40 On these two commandments hang all the Law and the Prophets.”

20 If someone says, “I love God,” and hates his brother, he is a liar; for he who does not love his brother whom he has seen, how can[c] he love God whom he has not seen? 21 And this commandment we have from Him: that he who loves God must love his brother also.

Jesus said to have eternal life we must love the Lord our God with all of our hearts, minds, and souls. That pretty much covers it all. Anyone who does that will not have a problem with any of the other commandments. But then Jesus adds another, that we must love our neighbors as ourselves. It seems the first commandment would have covered this, i.e. anyone who loves God like that will have no problem loving his neighbor as himself, so why does he add the second one? I think it gives us a way to test how we are doing on the first one. It is easy to believe that we really love God, but until there is something tangible to prove it, how can we know for sure?