(CG 3/151). That the aforesaid Assistance is called 'Grace,' and what is th... (Book 3. God, the End of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

THE grace which constitutes the state of grace is an effect of God's love. But the proper effect of God's love in man is to make man love God: for the chief effort of the lover is laid out in drawing the beloved to the love of him; and unless that succeeds, the love must be broken off.

2. There must be some union between those who have one end in view, as citizens in one State, and soldiers ranked together on the battlefield. But the final end to which man is led by the assistance of divine grace is the vision of God as He essentially is, which is proper to God Himself; and so God shares this final good with man. Man then cannot be led on to this end unless he is united with God by conformity of will, the proper effect of love: for it belongs to friends to like and dislike together, and to rejoice and grieve together. The grace then that constitutes the state of grace renders man a lover of God, as he is thereby guided to an end shared with him by God.

3. The grace that constitutes the state of grace must principally perfect the heart. But the principal perfection of the heart is love. The proof of that is, that every motion of the heart starts from love: for no one desires, or hopes, or rejoices, except for some good that he loves; nor loathes, nor fears, nor is sad, or angry, except about something contrary to the good that he loves.

4. The form whereby a thing is referred to any end assimilates that thing in a manner to the end: thus a body by the form of heaviness acquires a likeness and conformity to the place to which it naturally moves."> But the grace that constitutes the state of grace is a form referring man to his last end, God. By grace then man attains to a likeness of God. And likeness is a cause of love.

5. A requisite of perfect work is that the work be done steadily and regularly. That is just the effect of love, which makes even hard and grievous tasks seem light. Since then the grace that constitutes the state of grace goes to perfect our works, the said grace must establish the love of God within us.

Hence the Apostle says: The charity of God is spread abroad in our hearts by the Holy Ghost who is given to us (Rom. v, 5).