5 Mark well the counsel which the Holy Ghost gives us by Solomon: "Make straight paths for your feet, and order your ways aright. Turn not aside to the right hand nor to the left, but turn away your foot from the evil way; for the Lord knows the ways on the right hand, but those on the left are perverse. He will make your ways straight, and will direct your steps in peace." Now consider, my brethren, that in these words of Holy Scripture, if there were no free will, it would not be said, "Make straight paths for your feet, and order your ways; turn not aside to the right hand, nor to the left." Nor yet, were this possible for us to achieve without the grace of God, would it be afterwards added, "He will make your ways straight, and will direct your steps in peace."
Source: Letters (New Advent)