This is becoming more and more important. Churches should pay attention and act accordingly:
We recognize no other pastors in the Church than faithful pastors of the Word of God, feeding the sheep of Jesus Christ on the one hand with instruction, admonition, consolation, exhortation, deprecation; and on the other resisting all false doctrines and deceptions of the devil, without mixing with the pure doctrine of the Scriptures their dreams or their foolish imaginings.
To these we accord no other power or authority but to conduct, rule, and govern the people of God committed to them by the same Word, in which they have power to command, defend, promise, and warn, and without which they neither can nor ought to attempt anything.
As we receive the true ministers of the Word of God as messengers and ambassadors of God, it is necessary to listen to them as to him himself, and we hold their ministry to be a commission from God necessary in the Church.
On the other hand we hold that all seductive and false prophets, who abandon the purity of the Gospel and deviate to their own inventions, ought not at all to be suffered or maintained, who are not the pastors they pretend, but rather, like ravening wolves, ought to be hunted and ejected from the people of God.*
*Calvin: Theological Treatises (p. 32).