Galatians 2: 1-10:
Then after fourteen years, I went up again to Jerusalem, this time with Barnabas. I took Titus along also. I went in response to a revelation and, meeting privately with those esteemed as leaders, I presented to them the gospel that I preach among the Gentiles. I wanted to be sure I was not running and had not been running my race in vain. Yet not even Titus, who was with me, was compelled to be circumcised, even though he was a Greek. This matter arose because some false believers had infiltrated our ranks to spy on the freedom we have in Christ Jesus and to make us slaves. We did not give in to them for a moment, so that the truth of the gospel might be preserved for you. As for those who were held in high esteem—whatever they were makes no difference to me; God does not show favoritism—they added nothing to my message. On the contrary, they recognized that I had been entrusted with the task of preaching the gospel to the uncircumcised, just as Peter had been to the circumcised. For God, who was at work in Peter as an apostle to the circumcised, was also at work in me as an apostle to the Gentiles. James, Cephas and John, those esteemed as pillars, gave me and Barnabas the right hand of fellowship when they recognized the grace given to me.
2 Timothy 1: 13-14
What you heard from me, keep as the pattern of sound teaching, with faith and love in Christ Jesus. Guard the good deposit that was entrusted to you—guard it with the help of the Holy Spirit who lives in us.
Titus 1: 9-11
He must hold firmly to the trustworthy message as it has been taught, so that he can encourage others by sound doctrine and refute those who oppose it. For there are many rebellious people, full of meaningless talk and deception, especially those of the circumcision group. They must be silenced, because they are disrupting whole households by teaching things they ought not to teach—and that for the sake of dishonest gain.
Christ taught us to "watch out for false prophets" and to outwardly recognise them by their bad fruits (Matthew 7: 15-16). One way of ascertaining the false shepherds among the sheep is by testing and discerning their faithfulness to the orthodox teachings of the church. Those handed down to us by the foundation of the prophets and apostles. Those who call themselves the Lord's anointed and walk contrary to sound doctrine, refusing to submit to the apostolic authority of the church, are to be resisted, rebuked and if push comes to shove, excluded from the Christian community (2 Timothy 4:2, Titus 3:9-10).
Outside of the church community, there are no pastors, elders, deacons or bishops. False teachers may call themselves that, and wear these titles before their name, but by their lack of submission to God's Word they show themselves to be apostles of Satan. Unlike Paul, who for fear of running his race in vain, privately submitted to the apostles in Jerusalem. Recognising the authority given to James, Peter and John, Paul set before them the gospel that he preached to confirm that his ministry was ordained by Christ, so that they might extend to him the right hand of fellowship.
Apostleship comes by the Word, is built on the Word, and is to be forever tested and trained by the Word. That Word is Christ who calls people to the true ministry of his word, and sustains them in their priestly office in spite of hardships, persecution, beatings, imprisonment, etc. Those teachers who despise the way of the cross, and hold onto worldly authority for unjust gain and personal power, show themselves to be false shepherds, lifting up their own boasts and strange ideas. Letting the testimony about Christ decrease, while their greatness and cultish influence increases among the strays who follow them.
We walk among Satan's snares, and one person with mad ideas may destroy in a short time all that has been built up over many years by many true ministers laboring night and day. We learn this from experience, with great grief; yet we cannot do anything about it.
Since the church is such a soft and tender thing, and so soon overthrown, we must be quick to watch against these people with their mad ideas. When they have given two sermons or have read a few pages of the Holy Scriptures, they reckon they are in control of all learners and teachers and are answerable to no human authority. You can find many such people today, bold and impudent persons who because they have not been tried by temptations have never learned to fear God, nor had any taste of feeling of grace. Because they are empty of the Holy Spirit, they teach what they like best and such things as are plausible and pleasant to the common people. Then the uneducated multitude, longing to hear news, soon joins them. And many others who think themselves well versed in the doctrine of the faith and have been tempted to some extent are seduced by them.
Paul teaches us from his own experience that congregations that are won by great labour are easily and soon upset. We should watch very carefully against the devil's rangings everywhere, lest he come while we are asleep and sow weeds among the wheat. However watchful and diligent the shepherds may be, the Christian flock is in danger from Satan. Let us therefore watch carefully - first, every one for himself, and second, all teachers, not only for themselves, but also for the whole church, so that we do not enter into temptation.
Martin Luther, Commentary on Galatians.