Regardless if we think we are deserving or undeserving (which is the case), God’s work and blessings in the believer’s life is a complete package, because He already knows what will transpire between Him every child of His. This package was completed on the Cross when Christ said “it is finished” (John 19:30).
“Covenant” and “Grace” are not in opposition but in parallel, in that each lies within succession of one another. Grace established union, while Covenant pointed to fellowship within the pre-established union. Once union with God has been established, it cannot vary (Rom 11:29), but the fellowship within the union can and should, towards the “drawing nigh to God” (Jam 4:8), which can only “enter into the Holiest by the blood of Jesus” (Heb 10:19).
Union once established, provides potential for another equally significant realism; a progression of fellowship by way of, not conforming, but “being conformed” (Rom 8:29; 12:2)—“from glory to glory” (2 Cor 3:18); which fellowship is not mature early in our union and therefore must be learned. First, by example of the “schoolmaster”, which was the Law to Israel (Gal 3:24), who were in type, representative for all mankind; Then, by the Master of the school—Christ, via His Father’s “Grace” (v 25).
Israel’s union with God was not covenanted, for He established union with them - to be their God and them to be His people - before the Law was given (Gen 17:8; Exd 34:27, 28). The Law Covenant God made with them was not intended to provide for fellowship through adherence to it; but to reveal the way for fellowship through the concept required for His fellowship, which would come later; union first, then fellowship through revelation and regeneration by His Son and Spirit.
God prepared the Law with specifications that He knew no man cold keep without ever breaking it. Since only Christ could keep it perfectly, He was the One to complete it or “end it” (Rom 10:4). - “The Law was given for the sake of Christ, for it had not been given had it not been for Him; all its institutions, ordinances, and sacrifices, were on His account: they were all shadows of Him, and He the body and substance of them; He was the end or mark and scope at which they all aimed; every type looked to Him, and every offering directed the worshipper to Him.” - J Gill.
This is why it written that righteousness is “fulfilled”, not by us, but “in us” (Rom 8:4)—through Christ. He does not want fellowship by our obedience to law, as God exampled in Adam’s union; which union only produced a way to be with God, but not a way to be in Him; similar to the Apostles and believers who were with Christ, as opposed to eventually being in Him (Psa 94:20).
This is what is meant by the Law was a “schoolmaster”, in that it was only preparatory for concept, not provisional for application. The concept is desire for obedience out of love for God, because of His love for us; not out of desire to just avoid punishment by the breaking of a law, which may have been the original intent of many, until we learned that “the goodness of God leads you to repentance” (Rom 2:4). “The purpose of the commandment is love from a pure heart” (1 Tim 1:5), which the Law wasn’t intended to deliver (Rom 8:3). A pure heart cannot derive from anyone but the Lord, and then it’s used by Him to bear (show – John 15:8), not produce, fruit; for only the Vine can produce.
The tutoring of the Law is similar to the ministry of John the Baptist (Mat 3:3), which God used to lead us to union with Him. Even though God knew there would be times of breaking His covenant, it would not affect Israel’s union with Him, which was evidenced by His continual chastisements in causing them to desire His provisions again.
This was a union without fellowship with God, for “The way into the Holiest of All was not yet made manifest” (Heb 9:8); meaning, not the Priest approaching the Holy of Holies within this earthly tabernacle (2 Cor 5:1), but through Christ who has “not entered into the holy places made with hands, which are the figures of the true; but into heaven itself, now to appear in the presence of God for us” (Heb 9:24).
The breaking of a law does not separate one from the law Maker, but declares one to be guilty under it, as long as it exists (Gal 3:10). Instead of vacillating in the Law - through ourselves, God foreordained and planned for a consistency of fellowship with Him via Grace - through Christ.
I say the Law was only preparatory and not provisional, because “it was weak through the flesh” [old man or Adamic-nature} – (Rom 8:3). It was only “a shadow of good things to come” (Heb 10:1) which could only teach one to come “unto Christ” (Gal 3:24); then through Him the provision would be established concerning “the very image of the things” (Heb 10:1) of God. “For ye are not come unto the mount that might be touched” (Heb 12:18), “But ye are come unto mount Sion” (Heb 12:22; Mic 4:7).