Strange as it may seem, the danger today is greater for the fervent Christian than for the lukewarm and the self-satisfied. The seeker after God’s best things is eager to hear anyone who offers a way by which he can obtain them. He longs for some new experience, some elevated view of truth, some operation of the Spirit that will raise him above the dead level of religious mediocrity he sees all around him, and for this reason he is ready to give a sympathetic ear to the new and the wonderful in religion, particularly if it is presented by someone with an attractive personality and a reputation for superior godliness.
Now our Lord Jesus, that great Shepherd of the sheep, has not left His flock to the mercy of the wolves. He has given us the Scriptures, the Holy Spirit and natural powers of observation, and He expects us to avail ourselves of their help constantly. “Prove all things; hold fast that which is good,” said Paul (I Thess. 5:21). “Beloved, believe not every spirit,” wrote John, “but try the spirits whether they are of God: because many false prophets are gone out into the world” (I John:4:1). “Beware of false prophets,” our Lord warned, “which come to you in sheep’s clothing, but inwardly they are ravening wolves” (Matt:7:15). Then He added the word by which they may be tested, “Ye shall know them by their fruits.”
(Tozer, How to Try the Spirits).