For whatever reason, there are some who will tell you that the idea of the Trinity is not biblical. Consider that the Trinity is taught from the very beginning of the Bible.
In the beginning God created the heavens and the earth. The earth was formless and void, and darkness was over the surface of the deep, and the Spirit of God was moving over the surface of the waters. Then God said, “Let there be light”; and there was light. [Genesis 1:1-3 NASB]
Right from the beginning we have God, His Spirit and His Word. After all, what do you suppose God spoke?
He spoke His Word.
In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things came into being through Him, and apart from Him nothing came into being that has come into being. [John 1:1-3 NASB]
For by Him (Jesus) all things were created, both in the heavens and on earth, visible and invisible, whether thrones or dominions or rulers or authorities–all things have been created through Him and for Him. He is before all things, and in Him all things hold together. [Colossians 1:16-17 NASB]
The idea of a triune God is not something we can fully understand. That in no way should cast doubt on the reality of the Trinity.