Objection 1. It would seem that religion should not be preferred to the other moral virtues. The perfection of a moral virtue consists in its observing the mean, as stated in Ethic. ii, 6. But religion fails to observe the mean of justice, since it does not render an absolute equal to God. Therefore religion is not more excellent than the other moral virtues.
Objection 2. Further, what is offered by one man to another is the more praiseworthy, according as the person it is offered to is in greater need: wherefore it is written (Isaiah 57:7): "Deal thy bread to the hungry."
But God needs nothing that we can offer Him, according to Psalm 15:2, "I have said: Thou art my God, for Thou hast no need of my goods." Therefore religion would seem less praiseworthy than the other virtues whereby man's needs are relieved.
Objection 3. Further, the greater. the obligation to do a thing, the less praise does it deserve, according to 1 Corinthians 9:16, "If I preach the Gospel, it is no glory to me: a necessity lieth upon me." Now the more a thing is due, the greater the obligation of paying it. Since, then, what is paid to God by man is in the highest degree due to Him, it would seem that religion is less praiseworthy than the other human virtues.
On the contrary, The precepts pertaining to religion are given precedence (Exodus 20) as being of greatest importance. Now the order of precepts is proportionate to the order of virtues, since the precepts of the Law prescribe acts of virtue. Therefore religion is the chief of the moral virtues.
I answer that, Whatever is directed to an end takes its goodness from being ordered to that end; so that the nearer it is to the end the better it is. Now moral virtues, as stated above (5; 04, 7), are about matters that are ordered to God as their end. And religion approaches nearer to God than the other moral virtues, in so far as its actions are directly and immediately ordered to the honor of God. Hence religion excels among the moral virtues.
Reply to Objection 1. Virtue is praised because of the will, not because of the ability: and therefore if a man fall short of equality which is the mean of justice, through lack of ability, his virtue deserves no less praise, provided there be no failing on the part of his will.
Reply to Objection 2. In offering a thing to a man on account of its usefulness to him, the more needy the man the more praiseworthy the offering, because it is more useful: whereas we offer a thing to God not on account of its usefulness to Him, but for the sake of His glory, and on account of its usefulness to us.
Reply to Objection 3. Where there is an obligation to do a thing it loses the luster of supererogation, but not the merit of virtue, provided it be done voluntarily. Hence the argument proves nothing.
Source: Summa Theologica (New Advent)