Jesus was a staunch believer in the oneness of God. He came to re-enforce the old commandments. He said:

“Think not that I am come to destroy the law, or the prophets; I am not come to destroy, but to fulfill. For verily I say unto you, till heaven and earth pass, one jot or tittle shall in no wise pass from the law, till all be fulfilled.

“Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the Kingdom of heaven; but whosoever shall do and teach them, the same shall be called great in the Kingdom of heaven”. (Matthew 5:17-19)

God conlmanded the Israelites, according to the Old Testament:

“I am the Lord thy God, which brought thee out of the land of Egypt, from the house of bondage. Thou shalt have none other gods before me … Thou shalt not make thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath or in the waters beneath the earth”. (Deuteronomy 5:6-8)

Over and over again, the Old Testament has very explicitly and emphatically enjoined belief in one God:

“the Lord our God is one Lord”. (Deuteronomy 6:4)

If Trinity, which is so much stressed by Christianity today, had its basis on facts, it would have been explicitly stated in the Old Testament. On the contrary, the teachings of Moses urge us to believe in one God. Jesus earnestly championed for this unity of God, as the New Testament quotes:

“And Jesus answered him. The first of all the commandments is, Hear O Israel; the Lord our God is one Lord: And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength. This is the first commandment”. (Mark 12:29-30)

Moreover, Jesus said:

“And behold, one came and said unto him, ‘Good Master, what good thing shall I do, that I may have eternal life?’ And he said unto him. ‘Why callest thou me good? There is none good but one, that is God, but if thou wilt enter into life, keep the commandments'”. (Matthew 19:16-17)

Thus, Jesus strongly believed in the absolute oneness of God, and enjoined others to believe in it.