Humility.

He that loveth not his brother whom he hath seen, how can he love God whom he hath not seen?
I John 4:20

An excerpt from Andrew Murray’s Humility:

What a solemn thought, that our love to God will be measured by our everyday intercourse with men and the love it displays; and that our love to God will be found to be a delusion, except as its truth is proved in standing the test of daily life with our fellow-men. It is even so with our humility. It is easy to think we humble ourselves before God: humility towards men will be the only sufficient proof that our humility before God is real; that humility has taken up its abode in us; and become our very nature; that we actually, like Christ, have made ourselves of no reputation. When in the presence of God lowliness of heart has become, not a posture we pray to Him, but the very spirit of our life, it will manifest itself in all our bearing towards our brethren. The lesson is one of deep import: the only humility that is really ours is not that which we try to show before God in prayer, but that which we carry with us, and carry out, in ordinary conduct; the insignificance of daily life are the importance and the tests of eternity, because they prove what really is the spirit that possesses us. It is in our most unguarded moments that we really show and see what we are.