3 But your fellow-servant has treated you with contempt perhaps? Yes! And you have treated God with contempt oftentimes. And what comparison is there between a fellow-servant and the Lord? As to the former, when he was perchance in some way injured, he insulted you, and thou were exasperated. But you insult the Lord, when you are neither treated with injustice nor ill-will by Him, but receiving blessing of Him day by day. Consider, then, that if God chose to search out rigourously what is done against Him, we should not live a single day.
For the prophet says, “If You will be extreme to mark iniquity, O Lord, O Lord, who shall stand?” And, to pass by all those other things, of which the conscience of every sinner is aware, and of which he no has no human witness, but God only; were we to be called to account for those which are open and admitted, what allowance could we expect for such sins? What if He were to scrutinize our listlessness and negligence in our prayers; and how, while standing before God and supplicating Him, we do not exhibit even so much fear and reverence for Him as servants do toward their masters, as soldiers do toward their officers, as friends do toward friends? When you discourse with a friend, you give heed to what you are doing, but when waiting on God on account of your sins, and asking pardon for so many offenses, and thinking that you shall obtain forgiveness, you are often listless; and while your knees are lying on the ground, you suffer your mind to wander every where, in the market, or in the house, babbling the while with your mouth vainly and to no purpose!
And this we experience, not once or twice, but frequently! Did God then choose to scrutinize this alone, do you think that we could obtain pardon, or be able to find any excuse? Truly, I think not!
Source: Homilies on the Statues (New Advent)