You shall not hearken unto the words of that prophet, or that dreamer of dreams: for the LORD your God is testing you, to know whether you love the LORD your God with all your heart and with all your soul.
All Commentaries on Deuteronomy 13:3 Go To Deuteronomy 13
Augustine of Hippo
God is said to know even when he causes someone to know, as it has been written: “The Lord your God puts you to the test that he might know if you love him.” Now this manner of speaking does not mean that God does not know; rather, [it was said] in order that people might know how far they have progressed in the love of God—a thing which is not fully recognized by them except by way of the testings which come about. As for the expression “he puts to the test,” it means that God permits testing. Therefore when it is also said that God does not know, this means either that he does not approve (i.e., does not recognize [as conformable to] his discipline and teaching), as it has been said: “I do not know you.” Or [it means] that he causes people not to know for their own good, because it serves no useful purpose for them to know. Accordingly the text “the Father alone knows” is correctly grasped if understood to say that he causes the Son to know, and the text “the Son does not know,” if understood to say that the Son causes men not to know (i.e., does not disclose to them what would serve no useful purpose for them to know).