"After he had greeted them, he began to relate one by one the things which God had done among the Gentiles through his ministry. And when they heard it they began glorifying God; and they said to him, 'You see, brother, how many thousands there are among the Jews of those who have believed, and they are all zealous for the Law; and they have been told about you, that you are teaching all the Jews who are among the Gentiles to forsake Moses, telling them not to circumcise their children nor to walk according to the customs.'"
— Acts 21:19-21 (NASB)
The very first thing Satan tried to do to the Church is to Judaize it. If he can get believers to come to the false notion that they must live under both Covenants, he can marginalize, nominalize, and even vaporize them. Paul's earliest epistle to the Galatians primarily deals with this problem in the Early Church. Traditionally we would most likely associate this with Jehovah's Witnesses and Seventh-day Adventists, but it is a problem that has roared back in this present church age which often calls itself "Messianic" or the "Hebrew Roots Movement". I am not saying everyone who adopts these terms is automatically false, but it appears that very large percentages of claimants are attempting to get people to adopt a dual-covenant theology demanding that it is required to first convert to Judaism before being able to embrace Christianity.