The sum of the Christian life is to believe Jesus and love others. These two are so closely related that you could really condense the sole purpose down to, “Believe Jesus”. Once you begin to really and truly believe Jesus, that is when you really and truly can start to love others. You can tell if you honestly believe Jesus by observing how you treat others (1 John 3:7-8). But we need to be careful not to use this knowledge as a weapon against our neighbor — when we hear a truth and apply it to our neighbor before we apply it to ourselves, we don’t honestly believe Jesus — we are just collecting ammunition to sin.