We proceed to the second article thus:
1. It seems that purification of the heart is not an effect of faith. Purity of heart pertains mainly to the affections. But faith is in the intellect. Hence faith does not cause purification of the heart.
2. Again, that which causes purification of the heart cannot exist together with impurity. But faith exists together with the impurity of sin, as is obvious in those whose faith is unformed. Hence faith does not purify the heart.
3. Again, if faith were to purify the heart in any way, it would purify the intellect especially. But faith does not purify the intellect of dimness, since it knows things darkly. Hence faith does not purify the heart in any way.
On the other hand: it is said by Peter (Acts 15:9): "purifying their hearts by faith."
I answer: the impurity of anything consists in its being mixed with meaner things. We do not say that silver is impure if it is mixed with gold, but only if it is mixed with lead, or with tin. Now it is obvious that a rational creature is of greater worth than all temporal and corporeal creatures. A rational creature therefore becomes impure if it subjects itself to temporal things through love of them. But when it turns to what is above itself, that is, to God, it is purified from this impurity by movement in the opposite direction. The first beginning of this movement is faith. As it is said in Heb.11:6: "he that cometh to God must believe that he is." The first beginning of purification of the heart is therefore faith, which purifies from the impurity of error. If faith is itself perfected by being brought to its form through charity, it purifies the heart completely.
On the first point: things which are in the intellect are the principles of things which are in the affections, since it is good understood that moves the affections.
On the second point: even unformed faith excludes such impurity as is opposed to itself, such as the impurity of error, which is due to die inordinate adherence of the human intellect to meaner things, and to the accompanying desire to measure divine things in terms of sensible things. But when faith is brought to its form by charity it tolerates no impurity, since "love covereth all sins,"  as it is said in Prov.10:12.
On the third point: the dimness of faith has nothing to do with the impurity of guilt, but is due to the natural limitation of the intellect of man in his present state.
 Migne: "charity makes all things to be loved."