If anyone says, "I love God," yet hates his brother, he is a liar. For anyone who does not love his brother, whom he has seen, cannot love God, whom he has not seen. (1 John 4:20)
Do you remember another verse that this parallels? Ok, well this is somewhat of a reverse parallel, but nonetheless, here is the verse it reminds me of (this is a paraphrase):
Love the Lord your God with all your heart and alll your soul and all your mind and all your strength, and love your neighbor as yourself. All the law and the prophets hinge on these two things.
Jesus said that when he was asked which was the "greatest" commandment.
So when you look at the 1 John verse, it's somewhat of a parallel because John is describing how it really is a living out of the two commandments. If you love God, you will naturally love your brothers, because God is love, and God loves us, all of us, and if we love God we will love whom He loves, which is everyone.
Got that? :)
It is a pretty good reality check, this verse. I mean, it's so very easy to say "well come on, this person is just terrible. He's not reliable, he's cruel, he's the worst boss/coach/friend/teammate ever, so I just don't have to try to be a good Christian to him, because he's rejected everything I say; it's just not worth it."
But if you're saying that you follow Jesus, that you're a Chrstian, then a show of an absence of love for someone.... well that makes your "deep and meaningful" relationship with God an utter lie.
Because I'm guilty of this a lot.
Like, all the time.
But thank God we have a God who forgives. Who loves us even when we're the worst boss/coach/friend/teammate ever.