Matthew 22:36-40 New King James Version (NKJV)

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.’ ³⁸ This is the first and great commandment. ³⁹ And the second is like it: ‘You shall love your neighbor as yourself.’ ⁴⁰ On these two commandments hang all the Law and the Prophets.”

We are not loving God with all of our heart, soul, and might if we are not loving our neighbor as ourselves.  This is illustrated in this verse very well:

“Therefore, if you are offering your gift at the altar and there remember that your brother or sister has something against you, leave your gift there in front of the altar. First go and be reconciled to them; then come and offer your gift.”  ~Matthew 5:24-25

This is also supported by the old testament scripture that teaches us that obedience is better than sacrifice (1 Samuel 15:22), because we cannot sacrifice ourselves or an offering unto God knowing that we have not been obedient to his other great command to love our neighbor as we love ourselves.  God does not want us to come before him with false piety and righteousness when we have trespassed against or offended our neighbor.

Therefore if we cannot love our neighbor, we cannot love God.

~selah