Recapping a simple logical proof...

1. Isaiah saw the Lord God in His glory:

Isaiah 6:1-3 - In the year of King Uzziah's death, I saw the Lord sitting on a throne, lofty and exalted, with the train of His robe filling the temple. Seraphim stood above Him, each having six wings; with two he covered his face, and with two he covered his feet, and with two he flew. And one called out to another and said, "Holy, Holy, Holy, is the LORD of hosts, The whole earth is full of His glory."

2. Isaiah says there is only one God and Savior:

Isaiah 43:10,11 - "You are My witnesses," declares the Lord, "and My servant whom I have chosen, in order that you may know and believe Me, and understand that I am He. Before Me there was no God formed, and there will be none after Me. I, even I, am the Lord; and there is no savior besides Me."

Isaiah saw no other divine glory, spoke of no other divine glory, abhorred the idea of any other "god". For the testimony of Jesus is the spirit of prophecy (Revelation 19:10), and the Lord Jesus is the "God of the spirits of the prophets" (Revelation 22:6)

3. The apostle John clearly applies Isaiah's words about the Lord God to Jesus Christ:

John 12:37-43 - But though He had performed so many signs before them, yet they were not believing in Him; that the word of Isaiah the prophet might be fulfilled, which he spoke, "Lord, who has believed our report? And to whom has the arm of the Lord been revealed?" For this cause they could not believe, for Isaiah said again, "He has blinded their eyes, and He hardened their heart; lest they see with their eyes, and perceive with their heart, and be converted, and I heal them." These things Isaiah said, because he saw His glory, and he spoke of Him. Nevertheless many even of the rulers believed in Him, but because of the Pharisees they were not confessing Him, lest they should be put out of the synagogue; for they loved the approval of men rather than the approval of God.

God's ancient people recognized the many titles, offices, names, and attributes of their great God. They honored Him in the names they used in their society. There is one Divine Name applied in the Bible to only One Person, however -

Isaiah 7:14 - Therefore the Lord Himself will give you a sign: Behold, a virgin will be with child and bear a son, and she will call His name Immanuel.

And Who is Immanuel according to Matthew? What does His Name mean? Matthew quotes Isaiah and gives the Holy Spirit inspired translation -

Matthew 1:23 - Behold, the virgin shall be with child, and shall bear a Son, and they shall call His name Immanuel, which translated means, "God with us."

This is but one of the innumerable testimonies in Scripture to the identity of the One and Only Savior!

God is the Only One to Whom every knee will bow and to Whom every tongue will swear -

Isaiah 45:23 - "I have sworn by Myself, the word has gone forth from My mouth in righteousness and will not turn back, that to Me every knee will bow, every tongue will swear allegiance.

And Paul, also under Divine inspiration, says that the Lord Jesus will receive this universal recognition and worship -

Philippians 2:10 - ...that at the name of Jesus every knee should bow, of those who are in heaven, and on earth, and under the earth, and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father.

Yes, to the glory of the Father. Trinitarians wholeheartedly affirm the incomprehensible unity of the Father, Son and Holy Spirit! This is not to say that each One relates to the Others, or to God's people, in exactly the same way. The Father glorifies the Son also! (examples: John 8:18, Mat. 17: 1-8)

Who is the Mighty God?

Jeremiah 32:18 - ...who showest lovingkindness to thousands, but repayest the iniquity of fathers into the bosom of their children after them, O great and mighty God. The Lord of hosts is His name...

Deuteronomy 10:17 - For the Lord your God is the God of gods and the Lord of lords, the great, the mighty, and the awesome God who does not show partiality, nor take a bribe.

Isaiah 10:21 - A remnant will return, the remnant of Jacob, to the mighty God.

Although not a New Testament passage, the same Isaiah, in a prophetic utterance clearly referring to the Lord Jesus Christ, says -

Isaiah 9:6 - For a child will be born to us, a son will be given to us; and the government will rest on His shoulders; and His name will be called Wonderful Counselor, Mighty God, eternal Father, Prince of Peace.

Since all judgment is given to the Son, Who does James have in mind when he says:

James 4:12 A - There is only one Lawgiver and Judge, the One who is able to save and to destroy.

God's Word is sure. It's universal testimony in all parts is that Jesus Christ has come in the flesh, Immanuel - GOD WITH US.

What attribute, quality, title, name, or office which only Deity can have is NOT assigned by God the Holy Spirit, the "Inspirer" of the Scriptures, to Jesus the unique Son of the Father, in those Scriptures? Surely, not one of them!

Who can forgive sins, but God alone? In the ultimate sense, all of our sins are against Him. This is what the Psalmist intended when he said in Psalm 51:4 - "Against Thee, Thee only, I have sinned, And done what is evil in Thy sight." Yes, we humans can injure one another, but in the final analysis, we have sinned against Jehovah God whenever we sin!

Exodus 34:7 - ...Who keeps lovingkindness for thousands, Who forgives iniquity, transgression and sin; yet He will by no means leave the guilty unpunished, visiting the iniquity of fathers on the children and on the grandchildren to the third and fourth generations.

Mark 2:5-5 - And Jesus seeing their faith said to the paralytic, "My son, your sins are forgiven." But there were some of the scribes sitting there and reasoning in their hearts, "Why does this man speak that way? He is blaspheming; who can forgive sins but God alone?"

What a merciful, amazingly loving God! He forgives all the sins of those who come to Him by faith, and justifies them freely by His atoning death and victorious resurrection! The burden of guilt for sin is rolled away, the Christian has peace with God. He or she need not worry about living with Him forever, because that is not based on works. Jesus has fully paid the price for the forgiveness of His saints, and has provided a place in God's eternal heaven for each one. Praise be to the Lord God!