Isaiah reveals to us the truth of Yahweh's plan. I am the 'A' and the 'Z', the First and the Last, the Beginning and the End. When Yeshua returns He will bring with Him the rewards that belong to His bride. As Israel is His people and meant to be His cherished possession out of all the nations of the earth so too are those of us who profess faith in Yeshua and abide in His Torah. To abide in Yeshua is to abide in the Torah because they are one and the same.
Sin is transgression of the Torah of Yahweh.
If you continue to transgress God's Torah after you come to faith in Yeshua then you are making the sacrifice of Yeshua as if it is nothing. Because in rejecting the Torah you are rejecting the Messiah Yeshua. And what it says in verse 31 should make you pause, think and consider. You are what you are, not what you were.