What "law" do you think Paul is speaking of if not Moses' Law?
Regardless, it is Jesus alone who saves us when we first
repent and believe and therefore no good work/deed of our own could ever have atoned for Adam's sin. Only Jesus Christ could atone for Adam's sin. Only a Person who is both God and Man could ever atone for Adam's sin and thereby repair the relationship between God and man.
Titus 3:5
Gifts, including the gift of salvation, can be rejected at any time.
Christians who deliberately and grievously sin after they are saved are rejecting and profaning the blood of Jesus which saved them and so they are no longer saved. These evil Christians have rejected/denied Jesus by their own deeds/works.
By committing grievous sins, they denied/rejected Jesus' gift. Unless they repent of their grievous sins before death, they will receive vengeance from God instead of the eternal life which they had been expecting.
Hebrews 10:26-27
For if we sin deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a fearful prospect of judgment, and a fury of fire which will consume the adversaries. nkjv
Titus 1:16
They profess to know God, but they deny him by their deeds; they are detestable, disobedient, unfit for any good deed. nkjv
Matthew 10:33
but whoever denies me before men, I also will deny before my Father who is in heaven. nkjv
When they are judged, the evil Christians will be surprised to hear what Jesus has to say to them. However, it will be too late for them to repent of their evil deeds and so they will reap what they sowed.
Matthew 7:21-23
Not every one who says to me, ‘Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of my Father who is in heaven. 22 On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’ 23 And then will I declare to them, ‘I never knew you; depart from me, you evildoers.’ rsv
Galatians 6:7-8
Do not be deceived; God is not mocked, for whatever a man sows, that he will also reap. 8 For he who sows to his own flesh will from the flesh reap corruption; but he who sows to the Spirit will from the Spirit reap eternal life. rsv