The contrast here should be obvious to all. Once again we are shown that salvation is a gift of God. It is not God that is unrighteous. He has proved that over and over again. As we will see further on in this book, Israel has been cut off at the stump and the Gentiles have been grafted into the root through Jesus Christ.
Salvation is by faith as we see throughout this book. It is the gift of God, not of works lest any man should boast.
In verse 31 we see the result of ritualism. Religion without life is worthless. Most religions have not figured this out. Years ago the hymns were too “old fashioned” and we needed to liven things up. So more choruses were introduced and subtly but intentionally the music became more worldly. Then “Christian rock” was coined. It was never Christian but it was rock. Of course there is bluegrass and southern gospel, etc. All of it was designed to entertain and keep the younger generation coming. That crowd still has not realized that they are dead. Paul was directed to address this problem among the Jews, but it applies to Gentiles as well.
Israel had the law of righteousness. They were still observing some of the law but not by faith. They were just doing it as a ritual. They wanted to live as they pleased, but they wanted to look as though they were righteous. The Pharisees were the prime example of that. They drew from parts of the law but they corrupted it so bad that it was worthless. Jesus warned:

Matthew 15:5 But ye say, Whosoever shall say to his father or his mother, It is a gift, by whatsoever thou mightest be profited by me;
6 And honour not his father or his mother, he shall be free. Thus have ye made the commandment of God of none effect by your tradition.

God is so much wiser than man. He knows what is in the heart of man. Those who want to make a mockery of His gift of salvation may fool people now, but they will never fool God and the end of those is not good. In fact it is destruction.
As we see in verse 32, Israel was guilty of trying to work their way into God’s favour. They refused to hear the Word of God. They failed to see the blessing of surrendering to God and knowing His peace and forgiveness. They distorted the law and it became a stumblingstone to them.
In verse 33 we see that God knew all about this as well. No one can outsmart God. It is the fool who declares there is no God. Those who would take advantage of the grace and mercy of God have nothing now and nothing for eternity.
God directed the apostle Paul to quote two more Old Testament passages to finish off this chapter.

Isaiah 8:14 And he shall be for a sanctuary; but for a stone of stumbling and for a rock of offence to both the houses of Israel, for a gin and for a snare to the inhabitants of Jerusalem.

Isaiah 28:16 Therefore thus saith the Lord GOD, Behold, I lay in Zion for a foundation a stone, a tried stone, a precious corner stone, a sure foundation: he that believeth shall not make haste.