St. Thomas on Justification - We need grace in order to become good

Catholics believe what the Psalm says:

Lord, who shall dwell in thy tabernacle? or who shall rest in thy holy hill?

He that walketh without blemish, and worketh justice:

He that speaketh truth in his heart, who hath not used deceit in his tongue: Nor hath done evil to his neighbour: nor taken up a reproach against his neighbours.

In his sight the malignant is brought to nothing: but he glorifieth them that fear the Lord. He that sweareth to his neighbour, and deceiveth not;

He that hath not put out his money to usury, nor taken bribes against the innocent: He that doth these things, shall not be moved for ever. [Ps. 14/15]

We believe it moreso, perhaps, than Protestants seem to do, because we believe that we must be truly righteous - and not simply declared righteous - in order to see God's face. The difference is similar to that between a man who has never murdered, and a murderer who gets off in a trial despite his actual guilt: the latter man has been declared innocent although he really isn't. As the Psalm indicates, such a declaration would be totally inadequate for the hope of actually seeing God: the murderer is not righteous, no matter how often a court lets him off. The analogy is not quite perfect maybe, but the point is that we must be holy to see God, not merely declared, by way of what amounts to a legal fiction, to be "holy".

In ST I-II Q99 A2 ad 3, St. Thomas tells us that we need grace in order to keep the precepts of the moral law.

As Augustine proves (De Spiritu et Litera xiv), even the letter of the law is said to be the occasion of death, as to the moral precepts; in so far as, to wit, it prescribes what is good, without furnishing the aid of grace for its fulfilment.

If grace is necessary for the fulfillment of the moral precepts, then we cannot do so in our own strength. But if we cannot fulfill them in our own strength, then we cannot be holy in our own strength, and consequently we cannot see God's Face apart from his grace. And of course none of this addresses the related issue of the justification our sins require - a justification that we can in no way accomplish, achieve, or merit based upon anything we do (as we have seen repeatedly in this series).

So once again we see that the Catholic Church does not teach a works-based Gospel, notwithstanding the erroneous and misinformed complaints of Her critics.