That God sees and knows all things has a number of major implications for our lives in practice.
No Secret Sins
Job knew this, and therefore, he commented, it was impossible that, e.g., he would lust after a woman, if he really believed (as he claimed he did) that God was omniscient. ‘Why then should I think upon a young girl [as the friends implied he had done]?...does not he [God] see my ways, and count all my steps?’ (Job 31:4). Proverbs 5:20,21 makes the same warning against being “embraced in the arms of a seductress”, “For the ways of man are before the eyes of the Lord, and he ponders all his goings”. Also in the context of sexual sin, David could say that his awareness of his sin was ‘ever before him’ (Ps. 51:3); and also that he sensed God ‘ever before him’ (Ps. 16:8). A sense of the real presence of God leads us to an awareness of our sins. Likewise God had to remind Israel: "Can any hide himself in secret places that I shall not see him? ...do not I fill heaven and earth?" (Jer. 23:24). The context is appealing to the people to quit their sins. We should labour to enter the Kingdom, because God knows absolutely every thought and action of ours and will ultimately judge them (Heb. 4:11-13). The Sermon on the Mount is really based around translating the knowledge that God sees and knows all things into practice. Our thoughts are equivalent to our actions; and yet often we think that the fact we are clever enough not to express them in action is somehow a lesser failure. And yet God sees our thought afar off. Realizing this will help us avoid the greatest danger in the religious life: to have an outward form of spirituality, when within we are dead. Note how the Lord Jesus begins each of His letters to the churches with the rubric: " I know…" ; His omniscience of His people ought to motivate to appropriate behaviour. His criticisms of those ecclesias imply that they didn't appreciate the fact that He knew them and their ways. Hannah had reflected upon God's omniscience; and on this basis she tells Peninah not to be proud and not to use hard words against her, exactly because of this: " Talk no more so exceeding proudly; let not hardness [AVmg.] come out of your mouth: for the Lord is a God of knowledge, and by him actions are weighed" here and now, because He sees and knows all things (1 Sam. 2:3).
Fred Barling commented: "What God loves is the man who is genuine through and through; in whom the "without" and the "within" are really one; whose dominant persuasion is, "You God see me" " . The Hebrew language reflects certain realities about the nature of God's ways. The common Hebrew word for 'to see', especially when used about God's 'seeing', means also 'to provide'. Abraham comforted Isaac that "God will see for himself [AV 'provide'] the lamb" (Gen. 22:8 RVmg.); and thus the RVmg. interprets 'Jehovah-Jireh' as meaning 'the Lord will see, or provide' (Gen. 22:14). The same word is used when Saul asks his servants to "provide" him a man (1 Sam. 16:17). When Hagar said "You God see me" (Gen. 16:13), she was expressing her gratitude for His provision for her. What this means in practice is that the fact God sees and knows all things means that He can and will therefore and thereby provide for us in the circumstances of life; for He sees and knows all things.
Faith in Prayer
If God really does see and know all things, then He surely hears prayer. We raise our eyebrows when we read David’s desperate prayer: “Don't be deaf unto me” (Ps. 28:1). He who made the ear shall surely hear. God of course isn’t deaf- and just as surely and obviously, He will likewise hear prayer.