Dr. A. Kurt Weiss was an Austrian-born Jew and Holocaust survivor. He managed to make it to England, then the United States to Oklahoma Baptist in 1942. At 19 he was far from home with no money, friends or family. People in Shawnee immediately started praying for him, hoping to convert him to Christianity.
Several people indicated verses in the Old Testament that pointed to Jesus. Weiss remained resistant until another Austrian-born Jew visited him, Dr. Jacob Gartenhaus. Gartenhaus was Jewish, but also a Christian.
Eventually, in his own studies of the scriptures, Weiss came across what is widely considered one of the definitive verses in the Old Testament pointing to the Trinity: Isaiah 48:16.
Come near to Me, listen to this:
From the first I have not spoken in secret,
From the time it took place, I was there.
And now the Lord GOD has sent Me, and His Spirit.
– Isaiah 48:16 (NASB)
This verse, in fact indicates three people who are all God: the speaker, God, and the Spirit.
That did it for Weiss. He became a Hebrew Christian, and remained active in the faith the rest of his years.
BibleStudyTools has a list of 26 verses about the Trinity. God the Father, Son, and Holy Spirit are all one God. And praise God for that fact.
Dr. Weiss’s life details are from:
James C. Hefley, Adventurers with God: Fifteen Scientists Share Their Christian Faith, (Grand Rapids, MI: Zondervan, 1967).