The commandment of God is, that we love our Lord in all our heart, in all our soul, in all our thought. In all our heart; that is, in all our understanding without erring. In all our soul; that is, in all our will without gainsaying. In all our thought; that is, that we think on him, without forgetting. In this manner is very love and true, that is work of man's will. For love is a wilful stirring of our thought unto God, so that is receive nothing that is against the love of Jesus Christ, and therewith that it be lasting in sweetness of devotion; and that is the perfection of this life.
Richard Rolle: The Commandment.