What is then the perfection of which man is capable while he dwells in a corruptible body? It is the complying with that kind command, ‘My son, give me thy heart.’ It is he ‘loving the Lord; his God with all his heart, and with all his soul, and with all his mind.’ This is the sum of Christian perfection: It is all comprised in that one word, Love. The first branch of it is the love of God: And as he that loves God loves his brother also, it is inseparably connected with the second: ‘Thou shalt love thy neighbor as thyself:’ Thou shalt love every man as thy own soul, as Christ loved us. ‘On these two commandments hang all the Law and the Prophets: These contain the whole of Christian perfection.
Many more John Wesley quotes on the topic of Christian Perfection can be found here: THE NATURE OF CHRISTIAN PERFECTION. And here’s a link that will take you to the Table of Contents of John Wesley’s own compilation of his teachings on this topic: A Plain Account of Christian Perfection.
There is no perfection ‘which does not admit of a continual increase.’ However far a Christian may advance in sanctification ‘he hath still need to ‘grow in grace’, and daily to advance in the knowledge and love of God His Saviour.’ The gradual development, then, still continues. It is conceived primarily as further growth in love on the plane of entire sanctification. The Christian life must either wax or wane. It is impossible for the Christian, even if fully sanctified, to stand still. ‘Yea, and when ye have attained a measure of perfect love, when God has circumcised your hearts, and enabled you to love him with all your heart and with all your soul, think not of resting there. That is impossible. You cannot stand still; you must either rise or fall; rise higher or fall lower. Therefore the voice of God to the children of Israel, to the children of God, is, ‘Go forward’! ‘Forgetting the things that are behind, and reaching forward unto those that are before, press on to the mark, for the prize of your high calling of God in Christ Jesus’!’ The Christian, even the fully sanctified Christian, must still face the possibility of being lost. Thus even such a one must still be admonished to give up his attachment to the world.
— Harald Lindström, “Sanctification and the Order of Salvation” Wesley and Sanctification (1949).