The antithesis is between “destroy the Law” and “fulfill” or “complete” (TATIAN), not “destroy the Law” and “perpetuate the Law.”
The Ebionites, however, were a heretical sect who continued to keep the Mosaic Law (HIPPOLYTUS).
But the early Church understood that the New Covenant abrogated the Old and Jesus Christ gave a new law. An eternal and final law–
namely Christ–has been given to us (JUSTIN MARTYR).
Christ fulfilled the Law, therefore the Law and the prophets were with the Jews until John the Baptist (IRENAEUS, TERTULLIAN).
On the other hand, a leading heretical teacher of the second century, Marcion taught many Gnostic beliefs, including the belief that the God of the Old Testament was a different God from the Father of Jesus (TERTULLIAN).
The early Christians understood that Christ came as the anticipated Messiah to fulfill the promises of God from the Old Testament, not to destroy the message of the Old Testament. Christ did not come to destroy the Law but to fulfill, extend, and afford greater scope to it (IRENAEUS).
By His advent Christ fulfilled all things, and does still fulfill in the Church the new covenant foretold by the Law (IRENAEUS).
In keeping the commandments, Christ fulfilled the Law (HIPPOLYTUS).
All the Scriptures will be fulfilled because by the mouth of the Lord the Holy Spirit has spoken these things (CLEMENT OF ALEXANDRIA).
It behooves us to obey and do that which Christ did, and what He commanded (CYPRIAN).
We labor not only with words, but also deeds (CYPRIAN). The things which you teach cannot have any weight unless you shall be the first to practice them (LACTANTIUS).
We are exhorted to surpass the pharisaic way of living in order to be saved (JUSTIN MARTYR, CLEMENT OF ALEXANDRIA).
For extended discussion, see JUSTIN MARTYR (1.200-206).