What is the purpose of the Law?
17 “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18 For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished.
1 Corinthians 9:21
21 To those outside the law I became as one outside the law (not being outside the law of God but under the law of Christ) that I might win those outside the law.
24 So then, the law was our guardian until Christ came, in order that we might be justified by faith.
16 Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath. 17 These are a shadow of the things to come, but the substance belongs to Christ.
The three tier purpose of the Law summarized as taught by reformers, puritans, and historically in the church include:
(1) The Law of God is given as a tutor to lead us to Christ for the Law shows us our sin (Galatians 3:24).
(2) The Law communicate to us how to live in Christ (1 Thessalonians 4:1-8, Matthew 28:19-20, 1 Corinthians 9:21, Galatians 6:2).
(3) The Law is also given to restrain evil in society (Romans 13).
When we saw the Law we refer to the Law of Moses (the commands found in the Mosaic Covenant that God made with Israel).
The Law of Moses includes ceremonial, civil, and moral laws (Exodus, Leviticus, Numbers, Deuteronomy). All ceremonial and civil laws are a shadow of Christ and fulfilled in Christ (Matthew 5:17-20, Colossians 2:16-17, Mark 7:19, Acts 10, Acts 15) therefore they are not to be practiced in the New Covenant.
God is immutable (Malachi 3:6) and His standards of righteousness never change. Therefore, all moral commands of God are valid for the Christian to obey out of love for the one who saves not to earn salvation (John 14:15).
A Christian is saved by grace alone through faith alone in Christ alone to the glory of God alone revealed by the Scripture alone. A saved Christian out of a regenerated heart will deeply desire to follow the commands out of love for God (John 14:15, Psalm 119:97)