The trinity is a concept that God exists as 3 persons, that is, the Father, Son, and Holy Spirit.
Is there any indication or reference to the trinity in the Old Testament?
The concept of the trinity is nowhere to be found in God's inspired word the Bible. The dogma was formulated 300 years after the Bible was written. The formulation was refined under two Roman emperors with the urging of Catholic bishops.
I would disagree with you. At the baptism of Jesus, all three persons of the trinity were present: Matthew 3:16-17 And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him: And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
Notice also these verses: 1 John 5:7 For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.
Matthew 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
2 Corinthians 13:14 The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Ghost, be with you all. Amen...
I believe there is ample evidence to support the idea of a triune God. Welcome to the forum Alter!
Disagreeing with me isn't going to change the fact that the idea of a 3-in-1 god didn't show up in Christendom until 300 years after the Bible was written. Neither does your disagreeing with me change the
historical fact that the dogma was formulated under two Roman emperors (Emperor Constantine and Emperor Theodosius) -- both of them pagans -- and the fact that for political reasons they joined forces with the Roman Catholic bishops to insert pagan traditions into apostate Christianity.
Below are some facts about Roman Emperor Constantine's motive for getting involved with the Catholic bishops after the Catholic bishops began disputing over whether Jehovah (the Father) and Jesus Christ (the son) are equal. Focus on the words bolded in red and in blue. The weblink to the source will be at the end of the quotation.
"The dispute came to a head when the dynamic
theologian Arius, who was trained in Antioch, moved to Alexandria and became a priest at one of the local churches. He
taught that Christ was a created being subordinate to God the Father, and because he was created by the Father, there was a time when he did not exist.
This upset a rival priest named Athanasius who insisted that God was only one essence and Arius was teaching heresy. Athanasius complained to the local bishop, Alexander, and the fight became very intense.
"The dispute came to a head when the dynamic theologian Arius, who was trained in Antioch, moved to Alexandria and became a priest at one of the local churches. He taught that Christ was a created being subordinate to God the Father, and because he was created by the Father, there was a time when he did not exist. This upset a rival priest named Athanasius who insisted that God was only one essence and Arius was teaching heresy. Athanasius complained to the local bishop, Alexander, and the fight became very intense.
The religious glue that
Constantine had recently chosen to hold
his empire together
was tearing it
apart.
Something had to be done, so he called a counsel of bishops to be held in Nicaea in AD 325.
Typically, historians state that the orthodox position prevailed at this council, but that is true simply because that is the position that ultimately prevailed and became the orthodox position. The victors write the history. In reality, both Arius’s and Athanasius’s positions were extremes at the time. By far the dominant position was the Logos theology (described below), which had been the orthodox teaching of the Church for two to three centuries. This teaching fell in the middle of these two extremes and was referred to as Semi-Arianism and subordination Christianity. However, this position was too nebulous to end the debate and
satisfy the emperor’s need for a definitive conclusion to end the fighting. Ultimately,
the emperor chose Athanasius’s Trinitarian position at the Council of Nicaea, and
most of the bishops in attendance fell in line under threat of banishment."
See that? To summarize, because the bickering among the Catholic priests was causing division in the Roman empire, Emperor Constantine took sides with Athanasius' who believed Jehovah (the Father) and Jesus (the son) are equal. Keep in mind that at that point, the holy spirit was not even in the picture. At this point (325 C.E.) the dispute was over a 2-in-1 god. It would take decades before the idea of a 3-in-1 god would become the new version. That's where Emperor Theodosius (who succeeded Emperor Constantine) played his role.
I will address your "trinity" verses at another time.