In the days of the Apostle Paul no Jew or Gentile would have guessed that God would carry out his plan to reconcile the wayward world back into relationship with himself the way he did. Who would have guessed that God himself would enter into the lost world and inhabit a human body for 33 years only to be rejected by much of the world. Indeed we can say along with Paul…
God’s ways are Mysterious vv. 11:25-29
Lest you be wise in your own conceits, I want you to understand this mystery, brothers: a partial hardening has come upon Israel, until the fullness of the Gentiles has come in. 26 And in this way all Israel will be saved, as it is written, "The Deliverer will come from Zion, he will banish ungodliness from Jacob"; 27 "and this will be my covenant with them when I take away their sins." 28 As regards the gospel, they are enemies of God for your sake. But as regards election, they are beloved for the sake of their forefathers. 29 For the gifts and the calling of God are irrevocable.
Here Paul begins describing the age of Jesus and the New Covenant (the age we are still in today) when The fullness of the Gentiles will come in (v. 25). This begins with the spread of the gospel and the great response from Gentiles like in Acts with accounts like Cornelius the Roman soldier who trusts in Jesus through a vision and the teaching of Peter (Acts 10-11). Or Paul’s success in places like Athens (chpt. 17) and Ephesus and Corinth. It is evidenced by the Greco-Roman named recipients of this letter at the end Rom 15-16. It continues on to this day.
And Paul says that in this way “All Israel” will be saved (v. 26) What is the meaning of this phrase? We have already seen three places since chapter 9 (9:11, 14 & 11:7) where “Israel” does not mean all Israel but the chosen believers among Israel. The most recent again was in vs. 11:1 Paul’s answer to the rhetorical question, “Has God rejected his people?” using himself as an object lesson. In other words, God’s way of saving Israel is first, through providing Jesus the Messiah and all Jews who put their faith in Jesus the Jewish Messiah will be saved.
Secondly, now look at vs. 26 which says, and in this way all Israel will be saved.” What way? The tale of the two olive trees explains “in what way:” By grafting the Gentile “branches” into the original tree (Israel) and thereby making the original ethnic unbelieving Jewish branches jealous so some more come in through faith in Jesus. Those who are elect among Israel will be re-grafted in when they put their faith in their Messiah. So, then this is the entire new tree of cultivated (Jewish) and wild (Gentile) branches who together with later natural branches re-grafted back in make up “all Israel.” This is exactly what Paul has been making the case for in chpts 9-10 and will become the basis of Paul’s case in chapters 12-14 for why the Jewish-background believers and Gentile-background believers must accept one another and love one another. Because the gospel of Jesus Christ has made Jews and Gentiles into one new tree (an all New Israel called the Church), therefore, they must all accept each other as brothers and sisters in Christ.
But what if the Jews don’t accept this teaching? What if Paul is just making this up? Well in verse 26 Paul quotes from Isaiah 59:20-21 as his proof of this in-grafting of the two peoples into one tree. Here the “covenant” mentioned refers to the New Covenant brought by the first coming of Jesus. So, even Isaiah had prophesied at the coming of the Messiah, entrance to the Kingdom of God would through faith in the Messiah – this is the only door of entrance into the kingdom of God. Which means, according to Romans 10 entrance to the Kingdom only comes as a response to the preaching of the gospel (Rom 10:13- 17). “Paul is clearly relating the conversion of Israel to the process [already started] by the first coming of Christ and the subsequent preaching of the gospel…. The salvation of “all Israel” is already underway.”  This is all a great grand display of God’s glorious mercy. That is the next characteristic of God’s ways Paul describes.
God’s ways are Merciful (vv.30-32)
“Just as you were at one time disobedient to God but now have received mercy because of their disobedience; 31 so they too have now been disobedient in order that by the mercy shown to you they also may now receive mercy. 32 For God has consigned all to disobedience, that he may have mercy on all.”
Something we see God doing over and over again in the Bible is, in order to show and amplify his mercy and grace, is to show his mercy and grace to people who obviously don't deserve it. “Salvation is always given to those existing in disobedience.”  The nations (or Gentiles) were disobedient because they were ignorant of God and they received God’s mercy through the preaching of the gospel. The unbelief of the Jews is now, in a sense amplified in the coming of Jesus, the one door into God's Kingdom "and now disobedient Jewish Israel can receive mercy by way of the mercy shown to the Gentiles." God has worked all of what we call his “redemptive history” – the grand working of history to bring about a redeeming of a people to himself all to show his mercy. The grand and glorious conclusion stated in v. 32 is that God’s ultimate purpose is the universalization of his mercy. In other words, God shows his mercy to whomever he chooses. This is good news for us. That God delights in showing his mercy to anyone who will come to him through Jesus. Have you done that? My prayer is that you will in this way be grafted in and receive the mercy of God. The proper response to discovering and experiencing the ways of God is praise and worship of God – and that’s what Paul breaks out into in vv. 33-36.
“Oh, the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways! 34 "For who has known the mind of the Lord, or who has been his counselor?" 35 "Or who has given a gift to him that he might be repaid?" 36 For from him and through him and to him are all things. To him be glory forever. Amen.
Are you humbled before the God whose ways are…
2. Whose ways are Full of Grace?
3. Whose ways are Sovereign?
4. Whose ways are both Severe and Kind?
5. Whose ways are Mysterious?
6. Whose ways are Merciful?
If we are honest there is a trace of human sinful nature in all of us that wants to baulk at and mock the idea of such a God. I have heard people question whether such a description of God is really the biblical account. I was one of those people at one time. Some people may just reject outright such a description of God. That's because in general people don’t want God to be this way. People want to domesticate him and keep him private and under their control. They want a god who performs dutifully within their narrow scope of human reason. But the Foreknowing, full of Grace, Sovereign, Severe, Kind, Mysterious, and Merciful God is God as he reveals himself to be in the Bible. And believers in this God when experiencing his ways in their lives will rejoice with Paul singing what we find in vv. 33-36. It is my prayer for you that you will, with greater and greater confidence sing the very same praises of God as he reveals himself to be in the Bible.
 Holwerda, 173-4.