The answer to the OP is relatively simple. If we follow the "letter" it will cause death, but "those who are led by the Spirit of God are the sons of God" (Rom.8:14). The Greek for "sons" is in contrast to "children" in verses 16-17. "Children" shows only the source of their birth and makes them potential heirs. "Sons" is term for the mature who DO INHERIT.
The Law of Moses contains about 620 Laws. No man but Jesus was able to keep them. This Law is still valid for Israel, for it is a Contract. For the Christian, the Law is nailed to the cross. But the New Testaments contains about 2,400 commands for the Christian. They are God's Word but if you try to follow them like Israel had the Law, you will fail. All you have dome is address the flesh and it power (or lack of power). But if, as in Romans 8, starting with verse 2, turn to the Holy Spirit, Who dwells in the human spirit, for both instructions and the power to execute them, you will have applied "the Law of Life in Christ Jesus".
Does the New Testament command us to preach the gospel "to the uttermost parts of the earth"? Surely! But the Spirit said WHERE to Paul (Act.16:7). If Paul had preached at Bithynia would he be a hero or a rebel? The word of God commands Christian women to not have short hair. But HOW SHORT? Ask the Spirit in your spirit.