In doing external acts we must use a certain measure of discretion. The attitude of a religious man towards the acts by which he acknowledges God to be God, is quite different according as those acts are internal or external. It is principally in the internal acts, the acts by which he believes, hopes and loves that man’s good consists and what makes man good in God’s sight. Whence it is written, The kingdom of God is within you (Lk 17:21). Man’s good and what makes man good in God’s sight does not, principally, consist in external acts. The Kingdom of God is not meat and drink, says Saint Paul (Rm 14:17)
Whence the internal acts are as the end, the thing, that is to say, which is sought for its own sake; the external acts, through which the body is shown as God’s creature, are but as means i.e. , things directed to and existing for the sake of the end.
Now when it is a question of seeking the end we do not measure our energy or resource, but the greater the end the better our endeavour.
When on the other hand, it is a question of things we only seek because of the end, we measure our energy according to the relation of the things to the end. Thus a physician restores health as much as he possibly can. He does not give as much medicine as he possibly can, but only just so much as he sees to be necessary for the attainment of health.
In a similar way man puts no measure to his faith, his hope, and charity, but the more he believes,hopes and loves, so much the better man he is. That is why it is said, Thou shalt love the Lord thy God with thy whole heart and with thy whole soul, and with thy whole strength (Dt 6:5).
But in the external actions, we must use discretion and make charity the measure of our use of them.
Saint Thomas Aquinas +1274