Most Christians know what the greatest commandment of God is. In case you don't know, here it is, given when someone asked the Lord a question about it . . .
“Teacher, which is the great commandment in the Law?” And He said to him, “‘You shall love the Lord your God with all your heart, and with all your soul, and with all your mind. This is the great and foremost commandment. The second is like it, 'You shall love your neighbor as yourself.’ On these two commandments depend the whole Law and the Prophets.” (Matthew 22:36-40).
Did you notice that last sentence from Jesus? On those two commandments the WHOLE LAW AND THE PROPHETS DEPEND!
Let's put it even more simply. If I love God, I will not want to do anything to wrong Him. Period. In fact, He said, "If you love Me, you will keep my commandments." (John 14:15)
If I love you, I will not want to do anything to wrong you or anyone else. As the Apostle Paul puts it, "Love does no wrong to a neighbor. Therefore, love is the fulfillment of the Law." (Romans 13:10).
Now, there is quite a bit of unpacking to do there, and how we live out that love day by day. And in this life, none of us do it perfectly. But it begins by having a saving relationship with Christ, believing that He died on the cross for our sins, and rising again from the dead for our justification. Only then, through His indwelling Holy Spirit and empowerment, can we truly begin to love as God loves.