Why is the mixing of Law and Grace not the Gospel of Jesus Christ? Because the Old Covenant and the New Covenant are INCOMPATIBLE. Therefore the mixing of the two results the truth and reality of both being compromised and thus conceals the reason for both and also results in misunderstanding the written word of God and produces theological hog-wash. A correct understand of both Covenants and keeping each in its distinct rightful place is necessary to live in the freedom and reality of what Christ has DONE for us...it has nothing to do with what we can DO for Him.
The scriptures declare that the New Covenant is BETTER and DIFFERENT than the Old Covenant. “This is the covenant I will make with the people of Israel after that time,” declares the LORD . “ I will put my law in their minds and write it on their hearts. I will be their God, and they will be my people. No longer will they teach their neighbor, or say to one another, ‘Know the LORD ,’ because they will all know me, from the least to the greatest,” declares the LORD . “For I will forgive their wickedness and will remember their sins no more” (Jeremiah 31:33- 34
What is missing from the New that is in the Old? A little two-letter word is missing, one word that makes all the difference in the world between the two: There is no “if.” Concerning the promises and provisions of this New Covenant, God says, “I will…I will…I will…I will.” The responsibility rests completely on His shoulders. There is not a single responsibility placed on man's doing. NONE! Therefore, we can already identify the New Covenant as unconditional, because of the lack of an “if,” and unilateral, because all the responsibility is assumed by God. Man is not a part of the equation. Knowing that if these things are true, we can be confident that this New Covenant is also perpetual, eternal and unending...Why? Because without the possibility of human failure ending it, we can be confident the Lord’s promises will never fail because He never fails, He is eternal and unending. WOW! That my friend is what makes the Old incompatible with the New and any attempt to mix the two renders people from experiencing the POWER of the New.
The Old Covenant was continual, bilateral, temporal (until the coming of Christ) and two sided because it was based on man's performance, "If you do...I will do". However the New Covenant is unconditional, unilateral and eternal, in regard to all its clauses God says "I Will" (one sided) which makes it unconditional as far as man is concerned.
How can the Old, a conditional, bilateral, and temporal covenant ever be mixed and blended with the New, a unconditional, unilateral, and eternal Covenant? That’s why those who claim to be Law-keeping "Bible Knowers", picking verses from all over the Bible without taking into account the different covenants, end up creating an indigestible theological hog-wash. That's why so many believers are living in confusion instead of in peace, confidence,contentment and the power of New Covenant living.
These two covenants have never been invoked at the same time. And in the pure gospel of Christ they never will be...because religion does mix them lends to the proof that they are not preaching the gospel of Christ.