Ga 3:2 This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith? Ga 3:6 ¶ Even as Abraham believed God, and it was accounted to him for righteousness
The word “legalism” (sometimes used in a negative light) is not in the bible, the concept simply refers to keeping a law, Mt 5:17.
Jesus summarized the Law of God as Love for God and neighbor. The Law of Moses teaches a person that a sacrifice is necessary to obtain forgiveness of sins, Rm 10:4.
Under the New Covenant Christians have to confess sin to the sacrifice (Jesus), for forgiveness.
In this way the law us leads to Christ, Gal 3:24. Christ is the end or goal of the law.
Ro 10:4 For Christ is the end of the law unto righteousness to every one that believeth
Abraham believed (had faith in) God and was considered righteous – he did the right thing, 1 Jn 3:7.
Doing the “works of the Law” is not the right way to be made acceptable to God, even though the sacrifices had to be made for a person to be forgiven after they sinned in the Old covenant, Heb 10:8. They could have sacrificed forever but without faith in God it would not have been the right way to be acceptable to God.
Ga 5:4 Ye are severed from Christ, ye would be justified by the law; ye are fallen away from grace.
God’s grace teaches a person to deny ungodliness. The law of Moses however taught a person to be reconciled to God after they sinned by appealing to God through a sacrifice.
Jesus is the sacrifice under the New Covenant.
Many times people think they can be right with God by doing what they consider to be right in their own eyes or estimation. Doing what is right is insufficient unless it is accompanied by faith in God.
The first time something is done it becomes a precedent. Since Abraham originally exhibited “faith” and God accepted this, it can be said to be a law. The right way to be accepted by God was to have faith, Gen 15:6. However after a person sins they are/were no longer right before God. They had to appeal to God through a sacrifice to again be made right or righteous before God.
Ga 3:10 For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them. The law says they must have faith. They would still be under the curse of the law (or be guilty of breaking God’s law) unless they first came to God by faith, which means of course they must believe that God is and that He rewards those who diligently seek Him.
Heb 11:6 But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.
If a person tries to be acceptable to God by performing the “works mandated by the Law” but does not have faith, they have broken with precedent or broken the law and are cursed on account of their disobedience.