How do you distinguish between the OT laws that are binding on Christians, and those that aren't?
On Jesus Christ's Cross, for both Jews and Gentiles (John 11:51-52) of all times, the letter of the Old Covenant Mosaic law was completely and forever abolished (Ephesians 2:15-16, Colossians 2:14-17; 2 Corinthians 3:6-18), disannulled (Hebrews 7:18), rendered obsolete (Hebrews 8:13, Galatians 3:2-25, Galatians 4:21 to 5:8), taken away and replaced (Hebrews 10:9) by the better hope (Hebrews 7:19), the better covenant (Hebrews 7:22, Hebrews 8:6-12), the second covenant (Hebrews 8:7, Hebrews 10:9), of Jesus' New Covenant law (Galatians 6:2, John 1:17, Matthew 26:28, Hebrews 12:24, Hebrews 9:15), so that the law was changed (Hebrews 7:12).
All Christians, whether Jews or Gentles, of all times, are delivered from the letter of the Old Covenant Mosaic law and should not keep it (Romans 7:6; 2 Corinthians 3:6-18, Galatians 2:11-21), or have any desire to keep it (Galatians 4:21 to 5:8, Galatians 3:2-25). Christians keep the spirit of the Old Covenant Mosaic law (Romans 7:6) by loving others (Galatians 5:14, Romans 13:8-10), by doing to others as they would have others do to them (Matthew 7:12).
The New Covenant is a new law (Hebrews 7:12,18-19, Hebrews 10:1-23), consisting of Jesus Christ's New Covenant/New Testament commandments (John 14:15), such as those which He gave in the Sermon on the Mount (Matthew 5:19 to 7:29) and in the epistles of the apostle Paul (1 Corinthians 14:37). These commandments exceed in righteousness the abolished letter of the Old Covenant Mosaic law (Matthew 5:20-48), so there is no reason for any Christian to ever want to go back under it (Galatians 3:2 to 5:26). It was just a temporary schoolmaster (Galatians 3:24-25), a temporary shadow (Colossians 2:16-17), which God set up because of sins long after He had set up the original promise of the Abrahamic Covenant, and long before He brought this promise to fulfillment in Jesus' New Covenant (Galatians 3:16-29, Matthew 26:28).
The letter of the Old Covenant Mosaic law has been made obsolete by the New Covenant (Hebrews 8:13). For example, the letter of the Old Covenant Mosaic law required an Aaronic priesthood (Exodus 30:30), whereas the New Covenant replaced the Aaronic priesthood with the Melchisedechian priesthood (Hebrews 7:11-28). And the letter of the Old Covenant Mosaic law required animal sacrifices for sin (Leviticus 23:19), whereas the New Covenant replaced these with the one-time sacrifice of Jesus Christ Himself on the Cross (Hebrews 10).
The letter of the Old Covenant Mosaic law is the Hagar to the New Covenant's Sarah (Galatians 4:21-25). So those people, whether Jews or Gentiles, who try to keep the letter of the Old Covenant Mosaic law are like Ishmael, Abraham's son by a bondmaid (Galatians 4:22), who was cast out (Galatians 4:30), while those people, whether Jews or Gentiles, who keep the New Covenant are like Isaac (Galatians 4:28), Abraham's son by a freewoman (Galatians 4:22,31), who became his heir (Galatians 4:30b).
The letter of the Old Covenant Mosaic law, including the letter of its Ten Commandments, written and engraven in stones (2 Corinthians 3:7, Deuteronomy 4:13, Deuteronomy 27:8), was the ministration of death and condemnation (2 Corinthians 3:7,9). For example, see Leviticus 20:10, Exodus 31:14, and Numbers 15:32-36; and contrast these with the New Covenant's John 8:4-11 and Matthew 12:1-8.
The letter of the Old Covenant Mosaic law has been completely and forever done away (2 Corinthians 3:11), abolished (2 Corinthians 3:13b). But it is still able to spiritually blind some people as with a veil from beholding Jesus Christ (2 Corinthians 3:14-16), while the New Covenant is the ministration of the Spirit and righteousness (2 Corinthians 3:6,8-9b), which remains (2 Corinthians 3:11b), and which permits Christians to remove the veil and to behold Jesus (2 Corinthians 3:16-18, Mark 15:38, Hebrews 7:18-19, Ephesians 2:15-18, Colossians 2:14-17).
But a mistaken spirit of Pharisaism can still sometimes deceive even some Christians into thinking that they must keep the letter of the Old Covenant Mosaic law to be saved from hell (Acts 15:1,5), or to become perfect (Galatians 3:2 to 5:26). This is a false, cursed gospel (Galatians 1:6-9). For if any Christians are keeping any part of the letter of the Old Covenant Mosaic law thinking that they must do so in order to be saved from hell, or in order to become perfect, then Jesus Christ will profit them nothing. They have fallen from grace (Galatians 5:2-8).