Nothing escapes God's knowledge. This is proved by the witness of the Scriptures and the analogy of the sun, which, although created, yet by its light or heat enters into all things.
51. Next comes the answer to the question, whether God, not having failed to show care for His work, now fails to have knowledge of it? Thus it is written: “He that planted the ear, shall He not hear? He that made the eye, shall He not regard?”
52. This false idea was not unknown to the holy prophets. David himself introduces men to speak whom pride has filled and claimed for its own. For what shows greater pride than when men who are living in sin think it unfit that other sinners should live, and say: “Lord, how long shall the ungodly, how long shall the ungodly triumph?” And later on: “And yet they say, the Lord shall not see: neither shall the God of Jacob regard it.” Whom the prophet answers, saying: “Take heed, you unwise among the people: O you fools, when will you understand? He that planted the ear, shall He not hear? Or He that made the eye, shall He not see? He that rebukes the nations, shall He not punish?— He that teaches man knowledge? The Lord knows the thoughts of man that they are vain.” Does He Who discerns whatsoever is vain not know what is holy, and is He ignorant of what He Himself has made? Can the workman be ignorant of his own work? This one is a man, yet he discerns what is hidden in his work; and God— shall He not know His own work? Is there more depth, then, in the work than in its author? Has He made something superior to Himself; the value of which, as its Author, He was ignorant of, and whose condition He knew not, though He was its Director? So much for these persons.
53. But we are satisfied with the witness of Him Who says: “I search out the heart and the reins.” In the Gospel, also, the Lord Jesus says: “Why do you think evil in your hearts? For He knew they were thinking evil.” The evangelist also witnesses to this, saying: “For Jesus knew their thoughts.”
54. The idea of these people will not trouble us much if we look at their actions. They will not have Him to be judge over them, Whom nothing deceives; they will not grant to Him the knowledge of things hidden, for they are afraid their own hidden things may be brought to light. But the Lord, also, “knowing their works, has given them over unto darkness. In the night,” he says, “he will be as a thief, and the eye of the adulterer will watch for the darkness, saying, No eye shall see me; he has covered up his face.” For every one that avoids the light loves darkness, seeking to be hid, though he cannot be hid from God, Who knows not only what is transacted, but also what will be thought of, both in the depths of space and in the minds of men. Thus, again, he who speaks in the book Ecclesiasticus says: “Who sees me? The darkness has covered me, and the walls have hidden me; whom do I fear?” But although lying on his bed he may think thus, he is caught where he never thought of it. “It shall be,” it says, “a shame to him because he knew not what the fear of the Lord was.”
55. But what can be more foolish than to suppose that anything escapes God's notice, when the sun which supplies the light enters even hidden spots, and the strength of its heat reaches to the foundations of a house and its inner chambers? Who can deny that the depths of the earth, which the winter's ice has bound together, are warmed by the mildness of spring? Surely the very heart of a tree feels the force of heat or cold, to such an extent that its roots are either nipped with the cold or sprout forth in the warmth of the sun. In short, wherever the mildness of heaven smiles on the earth, there the earth produces in abundance fruits of different kinds.
56. If, then, the sun's rays pour their light over all the earth and enter into its hidden spots; if they cannot be checked by iron bars or the barrier of heavy doors from getting within, how can it be impossible for the Glory of God, which is instinct with life, to enter into the thoughts and hearts of men that He Himself has created? And how shall it not see what He Himself has created? Did He make His works to be better and more powerful than He Himself is, Who made them (in this event) so as to escape the notice of their Creator whenever they will? Did He implant such perfection and power in our mind that He Himself could not comprehend it when He wished?
Source: On the Duties of the Clergy (New Advent)