@Chelsea_Casali your question reminds me of Heb 11:6 that tells us that without faith it is impossible to please God, because anyone who comes to Him must believe that He is and he is the rewarder of those who seek Him. What this tells me is that it is His design that He remains hidden. The reason I see is that if we saw obvious proof of His existence then following Him would not be a walk of faith. Then we would then be walking in what we know to be true.
Once we come to know Him by faith we will want to please Him. How can we do that if our walk is not by faith? We need to pray that God will reveal Himself to your father in the manner of His choosing that your dad will have faith to accept Him, and begin to please God.