A.W. Pink -- John 10:5

And a stranger will they not follow, but will flee from him: for they know not the voice of strangers" (John 10:5). This is very important, for it describes a mark found on all of Christ’s sheep. A strange shepherd they will not heed. This can hardly mean that they will never respond to the call of the false shepherds, but that the redeemed of Christ will not absolutely, unreservedly, completely give themselves over to a false teacher. Instead, speaking characteristically, they will flee from such. It is not possible to deceive the elect (Matthew 24:24). Let a man of the world hear two preachers, one giving out the truth and the other error, and he can discern no difference between them. But it is far otherwise with a child of God. He may be but a babe in Christ, unskilled in theological controversies, but instinctively he will detect vital heresy as soon as he hears it. And why is this? Because he is indwelt by the Holy Spirit, and has received an "unction" from the Holy One (1 John 2:20). How thankful we should be for this. How gracious of the Lord to have given us this capacity to separate the precious from the vile!