St. Thomas on Justification - Justification is from God's Mercy, not Justice

In discussing the fact that every work of God is equally the work of each of the Persons of the Trinity, St. Thomas tells us that the justification of sinners is "naturally connected" with divine mercy.

Although every effect of God proceeds from each attribute, each effect is reduced to that attribute with which it is naturally connected; thus the order of things is reduced to "wisdom," and the justification of the sinner to "mercy" and "goodness" poured out super-abundantly. [ST I, Q45, A6, ad 3]

But if justification proceeds from God's mercy, it cannot be said that our salvation is a matter of justice in which God saves us because we somehow merit redemption. Therefore we are saved by God, not by anything that we do. So we see (yet again) that those who falsely charge the Church with holding to a works-based "gospel" are badly misinformed.