1) Sinners can never know God unless God reveals to them.
2) In God’s revelation, we still cannot FULLY know God because He is infinite, but we can know God in the ways He tells us.
3) We can know God in two ways: look at the universe (God’s creation) and read the Bible (God’s words).
4) The Creation tells us there is a Creator. The Bible tells us who God is (holy, love, etc.) and who we are (sinners), and what is the salvation (Jesus Christ).
5) As we read the Bible. It tells us there is ONLY ONE God; and the Father is God; and Jesus is God; and the Holy Spirit is God. Then the Father is not the Son, and the Son is not the Holy Spirit, and the Holy Spirit is not the Father. Instead of saying so many definitions, we use the term “Trinity”.
6) Our fallen logic and reasoning contradicts with the doctrine of the Trinity, but it is indeed the revelation of the Bible. For example, in Isaiah 45:21b-22, God says:
“There is no other God besides me, a righteous God and a Savior; there is none besides me. Turn to me and be saved, all the ends of the earth! For I am God, and there is no other.”
“our great God and Savior Jesus Christ” (Titus 2:13)
“our God and Savior Jesus Christ” (2 Peter 1:1)