Jesus call this as the second most important commandment firstly to show how important is to forgive and support one another with tender compassion, agreeing wholeheartedly and living as one the word of God.
And secondly to express how important is the first commandment: " Love the Lord your God with all you heart, with all your soul and all your mind".
Both commandments are strictly linked. We cannot accomplish one and fail to accomplish the other one.