We proceed to the fourth article thus:

1. It seems that grace is not the principle of merit through charity more principally than through other virtues. Labour is worthy of its hire, according to Matt.20:8: "call the labourers, and give them their hire.'' But every virtue is the principle of some labour, since a virtue is a habit of action, as was said in Q.55, Art.2. Every virtue is therefore equally a principle of merit.

2. Again, the apostle says (I Cor.3:8): "and every man shall receive his own reward, according to his own labour." But charity lightens labour rather than increases it, since "love makes every hard and heavy task easy, and almost as nothing," as Augustine says (De Verb. Dom., Sermo 9; De Tempt., Sermo 49). Charity is not then the principle of merit more principally than other virtues.

3. Again, the virtue which is most principally the principle of merit would seem to be the virtue whose actions are the most meritorious. Now the most meritorious actions seem to be those of faith and patience, or fortitude. This is apparent from the martyrs, who for their faith remained stedfast unto death with patience and fortitude. Other virtues are therefore the principle of merit more principally than charity.

On the other hand: our Lord says: "he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him" (John 14:21). Now eternal life consists in the manifest knowledge of God, according to John 17:3: "this is life eternal, that they might know thee the only true God." The meriting of eternal life therefore depends principally on charity.

I answer: there are two sources from which the meritorious character of a human action is derived, as may be understood from what we said in the first article. First and foremost, there is the divine ordination. This is the ground upon which an action is said to merit the good to which a man is divinely ordained. Secondly, there is the free will of man, which gives him the power to act voluntarily on his own part, more than any other creature. In regard to either source, the principle of merit depends especially on charity. For we must observe in the first place that eternal life consists in the enjoyment of God. The movement of man's mind towards the enjoyment of divine good is the proper action of charity, and it is the action of charity that directs all actions of the other virtues to this end, since charity commands the other virtues. The meriting of eternal life therefore depends primarily on charity, and secondarily on other virtues, in so far as their actions are directed by charity. It is apparent, also, that we do most willingly what we do out of love. Even in respect of the voluntary character essential to its nature, therefore, merit depends principally on charity.

On the first point: since charity has the ultimate end as its object, it moves the other virtues to act. A habit which relates to an end always commands the habits which relate to the means to it, as we explained in Q.9, Art.1.

On the second point: there are two ways in which a work may be laborious and difficult. It may be so because of its magnitude, which increases its merit. Charity does not lighten labour in this respect. On the contrary, it causes us to undertake the greatest works. As Gregory says, "charity is such that it does great works" {Hom. in Evang.30). But a work may also be laborious and difficult because of a fault in him who labours. Anything can be hard and difficult if it is not done readily and with a will. Such labour lessens merit, and is removed by charity.

On the third point: an act of faith is not meritorious unless faith works by love, as is said in Gal.5. Neither is an act of patience and fortitude meritorious unless performed through charity, according to I Cor.13:3: "though I give my body to be burned, and have not charity, it profiteth me nothing."