You can apprehend God, but you will never comprehend Him.
To "comprehend" means to understand someone or something completely. Your knowledge of that person, or subject, or thing, is comprehensive. All-surrounding. Exhaustive and thorough, to the ultimate degree.
To "apprehend" just means to understand. You don't need to know everything to know truth. You don't need to know everything there is possible to know about God, to have a relationship with God! Isn't that a wonderful truth?
Comprehend and apprehend aren't synonyms, though people use them as if they are. You and I will never comprehend the Lord, not even in heaven. We can apprehend Him -- know truth about Him -- but we will never comprehend Him -- grasp everything possible about Him in every respect. After all, God is a Trinity, eternal, and infinite! We would need to be God, to comprehend God.
But I thank God that we can understand Him, which is all we need to be able to do, to be saved and become His children. I thank God that we don't need to comprehend Him, in order to know Him!