The Tenth principle asserts that God is omniscient, i.e., He knows everything.
His knowledge, obviously, is completely unlike our knowledge. We acquire knowledge while "His knowledge is not something that can be separated from His esence...He and His knowledge and existence are One... This concept is beyond the power of speech to express, and beyond the power of the ear to hear. There is no way the human mind can comprehend it" (Maimonides MT, Yesode haTora 2:10).
What we do understand about God's knowledge, and which concerns us the most, is that God knows us intimately. The Creator knows all the thoughts and actions of man, as it is said, "He Who created all their hearts, knows all their deeds." (Psalm 33:15.)
In the words of Rabbi Hayim Pereira-Mendes : "Whatever we do or say or think, God knows. It is useless for us to try and deceive God by false excuses. God knows our thoughts. God knows what conduct should be expected of us by reason of our intelligence or education or environment. The greater our intelligence, the better our education, the more enlightened our environment, the higher are the ideals of conduct expected from us by God and by man. God has given us the power of discerning between right and wrong. He knows that we possess that power. Therefore we must use it rightly and wisely."
Beyond its philosophical value this principle signals primarily our ethical responsibility: we must live a life with the consciousness that God knows our thoughts, actions and intentions. We might easily deceive other human beings. Hide our negative intentions or plans behind words or rhetoric. But when it comes to God, there are no lies, excuses or pretensions. The more we become alert of God's omniscience, the easiest to live a life of righteousness. And vice-versa.