For the gifts and calling of God [are] without repentance.
Note 4 at Ro 11:29: In context, this is speaking about the future restoration of the Jewish nation. Paul was saying that even though the Jews had rejected God, the Lord was still going to bring His promises to the Jews to pass. This is an act of total grace on the Lord's part (see note 5 at Ro 1:5).
This scripture has a broader application too. Any calling, or gift to accomplish that calling, that the Lord gives an individual is without repentance. It means that regardless of what an individual does, God doesn't withdraw His gifts and callings. This is why some ministers who fall into sin can still see the supernatural gifts of God flow in their ministries.
That is not to say that living a life separated unto God is not important. It is very important. People who are living in sin are going to have their faith made shipwreck through their consciences (1Ti 1:19). They will begin to lose effectiveness. However, as much as they can operate in faith, the gifts and callings of God that they have received are still there and they will function.
Anything that you've ever received from God is still there; it just needs to be activated by faith.