If the trinity is a true doctrine why does the Bible in most scriptures make it hard to defend?

it is hard to defend because it didn't come into the picture until after the supposed death of Jesus. it is more defined now, but the initial doctrine comes from the visions of Saul of Tarsu, this vision took over the teachings of Jesus and replaced it with the divinity of Christ. Trying ti explain the duality of Christ is confusing because it is ridiculous