Psalm 110:4 (ESV): "4 The Lord has sworn and will not change his mind, "You are a priest forever after the order of Melchizedek."
If God has called and appointed you to ministry, He will by no means change His mind for the gifts and the calling of God are irrevocable (Ro 11:29). Jesus is our perfect example of this!
David writes a profound truth in this psalm revealed by the Holy Spirit...that God doesn't revoke His calling nor does He change His mind on His appointments. Jesus was called to be both High Priest and King of Israel. This is why Jews were so confused and thought perhaps there would be two Messiahs, a political Messiah, and a religious Messiah for the Levitical priests were not allowed to be involved in politics. However, like Melchizedek, whose name means "king of righteousness", the King of Salem (peace), who offered Abraham the first communion in the Bible (Gen 14:18), was both Priest and King. Jesus would be the same forever after the order of Melchizedek.
If God has called and appointed you to something He won't change His mind. You can disqualify yourself from a calling by rebelling against the authority of God as King Saul did, but repentance restores you. God will never say, "you've done it this time, that's it, I'm stripping you of your calling." Pastors who fall can be restored through repentance back to ministry and so can you because God doesn't change His mind on His calling and appointment for you. If you have given up on your calling, repent and turn back to God for empowerment and restoration. He will never quit on you and you should never quit on Him!
Father, amazing grace, how sweet the sound, that saved a wretch like me. Thank You Lord for calling us to salvation, for gifting and appointing us to ministry. May we never leave our calling for it is for a lifetime. If we have disqualified ourselves with sin may we repent and be restored. Help us not to grow weary in our calling Lord. Fill us with faith and strength to be faithful until You return we pray in Jesus' name, amen.