Grace changes a Christian's aims and delights. God will have the whole heart. We must not divide our love between him and sin. We must love God propter se, for himself, for his own intrinsic excellencies. We must love him for his loveliness.
Gold is loved for itself.
Christians should be like seraphim, burning in holy love. We can never love God so much as he deserves. The angels in heaven cannot love God so much as he deserves. It is called the labour of love. Mary Magdalene loved Christ, and poured her ointments on him.