The schoolmaster, or tutor, in its proper use and administration is only temporary; for every child grows to maturity and then goes on without a schoolmaster to carry on the more mature ventures and qualities of life. Therefore, the law of Moses was also a temporary restraint to the Jews that they would know righteousness and holiness only through signs, symbols, types, and ordinances.
The Jews, in their former position before Christ came, performed the commandments of the law, both ceremonial and moral, in order to be refrained from the conduct and attitudes of the Gentiles. They were God's chosen people, and they were to be separate.
They, however, did not understand the mystery of the Gospel until Jesus, their Messiah, had come and done his duty as High Priest, taught them verbally, and sent the Holy Spirit to lead them into all truth. When the Messiah came, he was to fulfill all the ceremonial law and meet the demands of the moral law. When, in his redemptive work on Calvary, Jesus brought to nothing the need for the law to be a schoolmaster, it was "done away" (See 2 Cor. 3:7, 11, 14).
Christ's fulfilling the law manifested that our justification is not by the law but completely by grace through faith (Eph. 2:8-9). The schoolmaster simply brought men up to the point where Christ was to be given as the ultimate sacrifice for our sins: the law pointed to Christ all along the way until Christ fulfilled the law. Then the law was no longer a necessary witness, but Christ himself became our witness through the Holy Spirit.
Before faith comes, we are all under the schoolmaster; for the law is the only instrument that we have to restrain our actions and to produce any level of guilt in our conscience. But after faith comes, we are no longer under the schoolmaster (the law) because of Christ: Heb 7:26 For such an high priest became us, who is holy, harmless, undefiled, separate from sinners, and made higher than the heavens.
Thus, by faith we are the children of God and not by the law. Acts 10:43 To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins.