Think how long [God] overlooked your faults before you were even saved; always loving you for what you should be. Treat your brother with the heart of Christ and look upon him with the eyes of Jesus.
Ask God to sanctify your natural affections. Most of them are full of selfishness and constant provocations of envy, jealousy, and strife. You have inordinate and passionate loves that are purely earthly even if not immoral; and if you walk in heavenly love, you must have them crucified and purified, and exchanged for holy affections which are raised above all bitterness and strife, and characterized by peace, unselfishness, gentleness, forbearance, and all the fruits of the Spirit.
Above all else, if you would walk in unity, ask Christ to crucify you. The greatest enemy to love is self. Learn to look not on your own things, but on the things of others, and consider every moment not how this is going to affect you, but how it is going to affect your brother and you will be kept in love and sweetness.
Keep the joy and sweetness of the Lord…Ask God to give you His joy and to keep it full, and you will find it easy to love. Take Christ’s love. He will put His own heart in you; He will enable you to love even as He loves. He who commanded it will make the command possible and enable you to realize it.
(A.B. Simpson, Christ in the Bible: Psalms)