11:15
The wrong way to look at Israel’s rejection is to see it as God’s final judgment upon them. It is not the end of the story, but one stage along the way. It would also be wrong to think “well, their rejection brought our reconciliation. If they are accepted back we might lost out”. Indeed it is a common human trait, including among Christians, to fear that someone else's blessing means that I will get less. In God’s kingdom we are not in a zero sum game. It is always good for someone else to be blessed. We need to watch our hearts very carefully, we can easily become envious of other’s success, and this is partly out of fear. In God’s kingdom when one is blessed all are blessed, so Israel’s acceptance (or re-acceptance) will be a time of immense blessing for all.
What is “life from the dead”? This can be taken in various ways. It could refer to the resurrection of the dead, taking the view that the return of Christ will occur soon after Israel’s return to Christ. Another view is that Israel, which for so long was spiritually dead, will be alive, will start to be the people God always intended her to be. Maybe both were in Paul’s mind. A large scale turning to Christ in Israel is a fundamental part of God’s plan and it will bring spiritual blessing to the earth.
As an aside, we need to recognise that whatever the precise details of the final return of Israel, many Jews never believed in Jesus, many Jews are lost.
11:16
Paul is alluding to Numbers 15:17-21 where it was talking about the firstfruits of the harvest being offered to the Lord. The offering of the firstfruits made the whole harvest holy. We can apply this principle in our lives. We should make God our first priority at the start of the day, we should make giving to Him our first concern in budgeting our money.Then the rest of the day, the rest of our money will be holy. Here Paul is likening the early fathers: Abraham, Isaac, Jacob, Moses etc to the first fruits and the root. All Christians recognise that these people were men of God and are a vital part of God’s plan, revealing who He is and His means of working. The Christian “religion” has Jewish roots. Jesus is not a radical departure from the Old Testament, but a radical fulfilment of the Old Testament. If Christianity did not have its Jewish roots it would be no religion at all, it would certainly not have anything to do with God’s plans.