What does the Holy Bible say about discernment and insight?

In St. John Cassian’s second Conference, we read, “Such is discretion, which is not only the ‘light of the body,’ but also called the sun by the Apostle, as it said ‘Let not the sun go down upon your wrath’ (Eph. 4:26). It is also called the guidance of our life: as it said ‘Those who have no guidance, fall like leaves’ (Prov. 11:14 LXX). It is most truly named counsel, without which the authority of Scripture allows us to do nothing, so that we are not even permitted to take that spiritual ‘wine which makes glad the heart of man’ (Ps. 53:15) … This I say is ‘solid food,’ which can only be taken by those who are full grown and strong, as it is said: ‘But solid food is for full grown men, who by reason of use have their senses exercised to discern good and evil’ (Heb. 5:14). And it is shown to be useful and necessary for us, only in so far as it is in accordance with the word of God and its powers, as is said ‘For the word of God is quick and powerful, and sharper than any two-edged sword, and reaching even to the dividing asunder of soul and spirit, of both joints and marrow, and a discerner of the thoughts and intents of the heart’ (Heb. 4:12) and by this it is clearly shown that no virtue can possibly be perfectly acquired or continue without the grace of discretion. And so by the judgment of the blessed Antony as well as of all others it has been laid down that it is discretion which leads a fearless monk by fixed stages to God, and preserves the virtues mentioned above continually intact, by means of which one may ascend with less weariness to the extreme summit of perfection, and without which even those who toil most willingly cannot reach the heights of perfection. For discretion is the mother of all virtues, as well as their guardian and regulator.”⁷⁶⁴

764 St. John Cassian, The Conferences 2.4 (NPNF II/11:309–310).