14 Run, my brethren, lest the darkness lay hold of you. Awake to your salvation, awake while there is time; let none be kept back from the temple of God, none kept back from the work of the Lord, none called away from continual prayer, none be defrauded of wonted devotion. Awake, then, while it is day: the day shines, Christ is the day. He is ready to forgive sins, but to them that acknowledge them; ready to punish the self-defenders, who boast that they are righteous, and think themselves to be something when they are nothing.
But he that walks in His love and mercy, even being free from those great and deadly sins, such crimes as murder, theft, adultery; still, because of those which seem to be minute sins, of tongue, or of thought, or of intemperance in things permitted, he does the truth in confession, and comes to the light in good works: since many minute sins, if they be neglected, kill. Minute are the drops that swell the rivers; minute are the grains of sand; but if much sand is put together, the heap presses and crushes.
Bilge-water neglected in the hold does the same thing as a rushing wave. Gradually it leaks in through the hold; and by long leaking in and no pumping out, it sinks the ship. Now what is this pumping out, but by good works, by sighing, fasting, giving, forgiving, so to effect that sins may not overwhelm us? The path of this life, however, is troublesome, full of temptations: in prosperity, let it not lift us up; in adversity, let it not crush us. He who gave the happiness of this world gave it for your comfort, not for your ruin.
Again, He who scourges you in this life, does it for your improvement, not for your condemnation. Bear the Father that corrects you for your training, lest you feel the judge in punishing you. These things we tell you every day, and they must be often said, because they are good and wholesome.
Source: Tractates on the Gospel of John (New Advent)