20 Let us not then be negligent of what is our life, but let us be in earnest; and do every thing, in order that we may be without an enemy, and so present ourselves at the sacred Table. For nothing—nothing, I repeat, of what God commands will be difficult, if we give heed: and this is evident from the case of those who are already reformed. How many used to be cheated by the habit of using oaths, and to fancy this practice extremely difficult of reformation. Nevertheless, through the grace of God, when you put forth but a little effort, you for the most part washed yourselves clean of this vice.
For this reason I beseech you to lay aside also what remains, and to become teachers of others. And to those who have not yet achieved it, but allege to us the length of time during which they were before swearers, and say that it is impossible for them to pluck up in a short time that which has been rooted for many years; I would make this answer, that where any precept among those commanded by God requires to be put in due practice, there is no need of length of time, nor of a multitude of days, nor an interval of years; but of fear only, and reverence of soul; and then we shall be sure to accomplish it, and that in a short time.
But lest you should suppose that I speak these things at random, take a man whom you think much addicted to swearing; one that swears more times than he speaks; hand this man over to me for only ten days, and if I do not rid him of all his habit in these few days, pass the severest sentence on me.
Source: Homilies on the Statues (New Advent)