For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in.  (26)  And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob:  (27 )  For this is my covenant unto them, when I shall take away their sins. 

Romans 11:25-27

Explanation:

In these verses Paul wants to reveal a “mystery”.  A mystery in the New Testament sense is a previously unrevealed truth that God was now revealing.  He says He wants the gentile readers to know this mystery because he doesn’t want them to be “wise in your own conceits”.  This was another reference to pride that they may have been tempted to feel.  He had already mentioned to the gentiles that they ought to be careful about thinking that they were something because God was working among them in verse (see Romans 11:18-20).
The mystery being revealed about Israel is what is called in this text the “blindness in part” of Israel.  God had allowed for blindness among His people for His missional purposes.  What were those purposes?  Here it is called the “fulness of the Gentiles”.  The idea of fulness is the idea of something filling up, or coming to some kind of completeness.  God has a plan to allow this hardening while many gentiles come to know him as Savior.
He wants the gentiles to know though that God is not through with Israel, as he stated in verse 1.  He says here “all Israel shall be saved”. Just because God is dealing with national Israel at a different level it doesn’t mean that he will not keep His promises to national Israel.  God does not have in mind here that every individual person who is ethnically Jewish will be saved, but rather God will keep His promises to Israel as nation and do for them what He has promised to do.  There will be a ruler again on the throne of David in Jerusalem where the Deliverer, Jesus, will rule and reign.  There will be many who come to know and recognize Christ as the Savior and Messiah.  They will follow Him as King.  There will be a spiritual repentance and turning back to God through repentance and faith in Jesus Christ.

Application:

• God keeps His promises.  You can trust God to do what He says He will do.  There is a time between the promise and the fulfillment, and we must trust Him in that time.
• God is a missionary God.  When God called “father Abraham” and made the promise to him, the promise was that in his seed all the nations of the earth would be blessed.  This promise is being fulfilled as the the missonary purposes of God to redeem people from every nation, tribe and tongue are coming to pass in the world today.  This was and is God’s plan.
• God wants us to be humble.  Salvation is available and all glory in it should go to God and not to us.  He should get the glory!

Response:

• Trust God.  You may be in a time between the promise and the fulfillment.  Remember, the just shall live by faith. 
• Be on God’s mission today.  God has asked us to join Him on His mission.  Proclaim the Gospel to someone today.
• Watch out for pride!  Find a way to humble yourself and glorify God in word and deed.