The possibility of the knowledge of God springs from God, in that He is Himself the truth and He gives Himself to man in His Word by the Holy Spirit to be known as the truth. It springs from man, in that, in the Son of God by the Holy Spirit, he becomes an object of the divine good-pleasure and therefore participates in the truth of God.
The Christian Church confesses on the one hand that God is the Incomprehensible One, but also on the other hand, that He can be known and that knowledge of Him is an absolute requisite unto salvation. It recognizes the force of Zophar’s question, “Canst thou by searching find out God? Canst thou find out the Almighty unto perfection?” Job 11:7. And it feels that it has no answer to the question of Isaiah, “To whom then will ye liken God? or what likeness will ye compare unto Him?” Isa. 40:18. But at the same time it is also mindful of Jesus’ statement, “And this is life eternal, that they should know Thee, the only true God, and Him whom thou didst send, even Jesus Christ,” John 17:3.
Louis Berkhof, Systematic Theology, II. The Knowability of God - A. God Incomprehensible but yet Knowable
Because God is infinite and we are finite or limited, we can never fully understand God. In this sense God is said to be incomprehensible where the term incomprehensible is used with an older and less common sense, “unable to be fully understood.” This sense must be clearly distinguished from the more common meaning, “unable to be understood.” It is not true to say that God is unable to be understood, but it is true to say that he cannot be understood fully or exhaustively.
Wayne Grudem, Systematic Theology (1994), Ch. 10. The Knowability of God
O the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways!
Paul, Romans 11:33
Great is the Lord, and greatly to be praised; his greatness is unsearchable.