6 Decline, therefore, neither to the right hand nor to the left, although the paths on the right hand are praised, and those on the left hand are blamed. This is why he added, "Turn away your foot from the evil way,"--that is, from the left-hand path. This he makes manifest in the following words, saying, "For the Lord knows the ways on the right hand; but those on the left are perverse." In those ways we ought surely to walk which the Lord knows; and it is of these that we read in the Psalm, "The Lord knows the way of the righteous, but the way of the ungodly shall perish;" for this way, which is on the left hand, the Lord does not know.
As He will also say at last to such as are placed on His left hand at the day of judgment: "I know you not." Now what is that which He knows not, who knows all things, both good and evil, in man? But what is the meaning of the words, "I know you not," unless it be that you are now such as I never made you? Precisely as that passage runs, which is spoken of the Lord Jesus Christ, that "He knew no sin." How knew it not, except that He had never made it? And, therefore, how is to be understood the passage, "The ways which are on the right hand the Lord knows," except in the sense that He made those ways Himself,--even "the paths of the righteous," which no doubt are "those good works that God," as the apostle tells us, "has before ordained that we should walk in them"?
Whereas the left-hand ways--those perverse paths of the unrighteous--He truly knows nothing of, because He never made them for man, but man made them for himself. Wherefore He says, "The perverse ways of the wicked I utterly abhor; they are on the left hand."
Source: Letters (New Advent)