"Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace." Gal 5:4 (KJV)
That verse is referring to The Law of Ordinances that regulated the priesthood and the rites and sacrifices that went with the Levitical Priesthood. (Those laws were abolished at the cross of Jesus Christ.) No law can forgive sins (justification). No law can deliver us from the power of our sin nature. We must have faith in Jesus Christ!
The saints of the Old Testament also had faith and believed the gospel! Every time they offered a lamb, they were looking forward to "The Lamb of God that taketh away the sins of the world."
Old traditions are hard to give up! For centuries, natural Israel had offered the sacrifices of the "yoke of bondage." and some Jewish Christians were still doing those works of the law.
In the verse above, Paul is exhorting them to stop doing the carnal ordinances because all the promises of God are fulfilled in Christ.
The scriptures teach us that once we are forgiven, we must submit ourselves to the Lordship of Christ. We do that by obeying His Commandments.
(Here is a good opportunity for me to compare The Law Of Ordinances with The Ten Commandmants.)
1. The Law of Ordinances is the carnal law.
"The Holy Ghost this signifying, that the way into the holiest of all was not yet made manifest, while as the first tabernacle was yet standing:
Which was a figure for the time then present, in which were offered both gifts and sacrifices, that could not make him that did the service perfect, as pertaining to the conscience;
Which stood only in meats and drinks, and divers washings, and CARNAL ORDINANCES, imposed on them until the time of reformation." Heb 9:8-10 (KJV)
2. The Ten Commandments is the spiritual law. (It is the law that defines sin):
What shall we say then? Is the law sin? God forbid. **Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, THOU SHALT NOT COVET. Rom 7:7 (KJV)
"For we know that the law is spiritual: but I am carnal, sold under sin." Romans 7:14 KJV)
"That the righteousness of **the law might be fulfilled IN US**, who walk not after the flesh, but AFTER THE SPIRIT. Rom 8:14 (KJV)
"For as many as are led by the Spirit of God, they are the sons of God." Rom 8:14 (KJV)
Conclusion: The Law of Ordinances was abolished at the cross. Sin is transgression of The Ten Commandments. We must have faith in the death, burial and resurrection of Jesus for the forgivenss of sins. Christians must obey The Ten Commandments for Jesus to be our Lord. The sons of God obey The Ten Commandments through the enabling power of The Holy Spirit.