The doctrine of Christ is not an innovation of Christianity, not even a doctrine coined by Jesus Himself.
No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father. John 10:18
Believest thou not that I am in the Father, and the Father in me? the words that I speak unto you I speak not of myself: but the Father that dwelleth in me, he doeth the works. John 14:10
The doctrine of Christ is found scattered in the writings of the Law, the prophets, and the psalms,
And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself … 44And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. Luke 24:27, 44
All the references cited in the four Gospels recognize a difference in the teachings of Jesus from those known at that time, but they also recognize that such teachings belong to the Law, the Prophets, and the Psalms.
Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment: 22But I say unto you, … Matthew 5:21, 22
Ye have heard that it was said by them of old time, Thou shalt not commit adultery: 28But I say unto you, … Matthew 5:27, 28
Ye have heard that it hath been said, An eye for an eye, and a tooth for a tooth: 39But I say unto you, … Matthew 5:38, 39
Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy. 44But I say unto you, … Matthew 5:43,44
And it came to pass, when Jesus had ended these sayings, the people were astonished at his doctrine: 29For he taught them as one having authority, and not as the scribes. Matthew 7:28, 29
But in vain they do worship me, teaching for doctrines the commandments of men. Matthew 15:9
Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees. Matthew 16:12
Therefore, the doctrine that Jesus proclaimed is not a new doctrine originated in Him or by Him, His doctrine it was elaborated starting from the statutes of Mosaic Law, from prophecy of the prophets and in the singing praises of Psalms.
The religious departed from the spiritual teaching and added their own interpretations, far from the purposes for which it was established. That was the reason why Jesus constantly rebuked them, because they saw it more important to keep their tradition than to take care to put into practice the Word of God. Jesus regains the real emphasis and establishes the true spiritual value of its promulgation.
This is the part of the teachings about Jesus that many have not understood in relation to the validity of the Old Testament for the New Testament church. The majority of the contemporary faith communities have decided to renounce to the Veterotestamentary teachings, arguing that everything of the Old Testament no longer has validity on the Grace, incurring without knowing it in the greatest doctrinal error of the present time, and unfortunately, exposing themselves also to apostasy. All of them ignore that the, Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him (1st. Corinthians 2:9), to which the apostle Paul refers, are mysteries of Revelation still found in the Old Testament.