John 14:26: But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring in your remembrance all that I said to you.
In this scripture, Jesus clearly speaks of himself, the Father, and the Holy Spirit as separate persons. If they were not, he would have said something like this.
When I return as the Helper, the Holy Spirit, in my name and by my divine authority, I will teach you all things, and bring in your remembrance all that I said to you while I was clothed in flesh.
Jesus was not in the business of hiding things, so my conclusion is that Jesus, the Father, and the Holy Spirit are three persons.
Jesus also says, "Before Abraham, I am." (ego eimi) The expression in the Greek is purposeful and seen in the light of the Mosaic statement "Tell them I am has sent you." is a claim to diety by Jesus Christ. This is supported by many other scriptures both in the gospels and the epistles.
Then you have the Sch'ma: Hear O Israel, the Lord your God, the Lord alone. This is a statement of the uniqueness and the fundamental unity of God.
Put these three things together and what do you get: a Tri-Une God.
Other options: 1. Jesus spoke deceptively. What is clearly represent as three persons is actually one. Not acceptable.
2. Jesus was not God. Not supported by scripture. The Jews understood him clearly and picked up stones to stone him fof blasphemy.
3. God is not one. this would destroy the veracity of all scripture and of our faith.