1 Corinthians 11:19 says, For there must be also heresies among you, that they which are approved may be made manifest among you.
There is a heresy called Tritheism that defends itself by calling the opposing emphasis on the Oneness of God heresy; even though the one who is emphasizing that Oneness is not denying that God is distinctly three Persons (and yet One).
In Acts 24:14 Paul the apostle said, But this I confess unto thee, that after the way which they call heresy, so worship I the God of my fathers, believing all things which are written in the law and the prophets.
The true Trinity is held to be heretical by those who think that they believe in the Trinity and yet in all reality they believe in Tritheism. It should be clear from the holy scriptures that there is one God.
Deuteronomy 6:4, Hear, O Israel, The LORD our God is one LORD.
Mark 12:29, And Jesus answered him, The first of all the commandments is, Hear, O Israel; The Lord our God is one Lord.
Notice here that the Lord is God. And also, we have the following statement in Matthew 11:25:
At that time Jesus answered and said, I thank thee, O Father, Lord of heaven and earth, because thou hast hid these things from the wise and prudent, and hast revealed them to babes.
Again, scripture teaches that there is one Lord...
Ephesians 4:5, One Lord, one faith, one baptism.
1 Corinthians 8:6, But to us there is but one God, the Father, of whom are all things, and we in him; and one Lord Jesus Christ, by whom are all things, and we by him.
Now here there is one God, and a Lord separate from Him, if the Lord isn't God (the Father). However, we have already seen that the Lord our God is one Lord (Mark 12:29) and that the Father is the Lord of heaven and earth. This one Lord is the God who created us, Jesus Christ; and I contend here faithfully that He is the Father.
Isaiah 9:6-7, For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, the everlasting Father, The Prince of peace. Of the increase of his government and peace there shall be no end, upon the throne of David, and upon his kingdom, to order it, and to establish it witrh judgment and with justice from henceforth even for ever. The zeal of the LORD of hosts will perform this.
Luke 10:21, In that hour Jesus rejoiced in spirit, and said, I thank thee, O Father, Lord of heaven and earth, that thou hast revealed these things to the wise and prudent, and hast revealed them to babes: even so, Father; for so it seemed good in thy sight.
Jesus is the Lord:
1 Corinthians 12:3, Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed: and that no man can say that Jesus is the Lord, but by the Holy Ghost.
There is one Lord:
Ephesians 4:5, One Lord, one faith, one baptism.
That Lord is the Father:
Matthew 11:25, At that time Jesus answered and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes.
Luke 10:21, In that hour Jesus rejoiced in spirit, and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes: even so, Father, for so it seemed good in thy sight.
If anyone does not have the Holy Ghost, they do not belong to Christ:
Romans 8:9, But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
No one can say that Jesus is the Lord except by the Holy Ghost:
1 Corinthians 12:3, Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed: and that no man can say that Jesus is the Lord, but by the Holy Ghost.
The Father is the Lord:
Matthew 11:25, At that time Jesus answered and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes.
Luke 10:21, In that hour Jesus rejoiced in spirit, and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes: even so, Father, for so it seemed good in thy sight.
So I think that I have made it clear that there is a Oneness between the Father and the Son:
John 10:30, I and my Father are one.
It should be clear that both Jesus and the Father are the one Lord of scripture.