The answer
While Catholicism try to use reason to know God, Orthodoxy teaches that the knowledge of God cannot be reached unless God speaks to us. Human reason by itself is limited. God's thoughts, personality, and attitudes can only be known if God chooses to reveal them. We would be at a loss if God did not wish to be known. But God wants us to know Him; and has told us in the Holy Bible all we need to know about His character and how to relate to Him. We read in the holy book of Hebrews, "But without faith it is impossible to please Him, for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him" (Hebrews 11:6).
But this is not blind faith, it is a logically defensible faith. In fact, evolutionists who deny God are the ones who have a blind faith, they have to believe something that is against real science, namely that information can arise by chance from disorder. Christians can use logic to prove God's existence. This is why the Holy Bible makes it clear that anyone who does not believe in God is without excuse (Romans 1:20).
Isaiah 1:18 is not talking about man's reason in knowing God. It is God talking to man, reasoning with him meaning "to come to a legal decision". People were to come to an agreement with God concerning the enormous gravity of their sin. This has nothing to do with reason concerning the knowledge of God.
Hebrews 11:1 defines Faith (not Reason) as the evidence of things unseen. The saving knowledge of God comes through our Savior. Speaking to His Father, our Lord Jesus Christ said, "And this is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent" (John 17:3).
Answered by His Eminence Metropolitan Youssef (opens in a new tab)