Of Sheep, Thieves, and Shepherds; Sheep Know The Truth When They Hear It

Joh 10:27 My sheep hear my voice, and I know them, and they follow me:
Joh 10:28 and I give unto them eternal life; and they shall never perish, and no one shall snatch them out of my hand. 

Joh 10:2 But he that entereth in by the door is the shepherd of the sheep.
Joh 10:3 To him the porter openeth; and the sheep hear his voice: and he calleth his own sheep by name, and leadeth them out.
Joh 10:4 When he hath put forth all his own, he goeth before them, and the sheep follow him: for they know his voice.
Joh 10:5 And a stranger will they not follow, but will flee from him: for they know not the voice of strangers.
Joh 10:14 I am the good shepherd; and I know mine own, and mine own know me,

“Mine own know Me” but they “know not the voice of strangers.” Strangers G245 allotrios; means another’s, that is, not one’s own; foreign, not akin, hostile: – alien, other (man’s, men’s), strange (-r). To “know” G1097, means – get a knowledge of, perceive, feel; to understand, to become acquainted with. It’s also a Jewish idiom for sexual intercourse between a man and a woman; thus the term indicates an intimate knowledge of, or being ‘close’ to someone. This Greek term is synonymous with the Hebrew “yada” which has a rich range of meaning, including ‘care, recognition, observation, instruction; familiar friend, kinsfolk, kinsman, have respect for, understand, comprehend, and more. The idea in these passages, is that the sheep of Jesus Christ recognize his voice. They not only recognize His voice, but understand and comprehend what His will is, and do it. Obedience is the key to entering the kingdom of heaven, not prophesying, working of miracles, signs or wonders –
Mat 7:21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father who is in heaven.
Mat 7:22 Many will say to me in that day, Lord, Lord, did we not prophesy by thy name, and by thy name cast out demons, and by thy name do many mighty works?
Mat 7:23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
‘iniquity’ G458 anomia; without law, lawless, transgressor, unlawful, wicked. According to this definition, those who live in consistent disobedience to God’s words, are considered to be ‘lawless transgressors’ and ‘wicked.’ Transgressors won’t enter the kingdom of heaven, Jesus said. It’s a critical point, one not to be taken lightly, for Jesus always means what he says. Of course, what is meant are willful and consistent transgressors; those who make a lifestyle of reckless living, going against God’s revealed will in the Bible, not godly persons who repent when they transgress. To sum up, those who mistakenly think that they have a ticket to heaven because they speak in tongues, prophesy, cast out demons, work miracles and other mighty works, but consistently lived in disobedience to God’s words, will be sorely disappointed. Charisma, charm, intelligence, having a license to preach, being a deacon, pastor, or choir master – won’t gain you entry into the kingdom of heaven either. Obedience to God’s word, is the key to entering the kingdom of heaven. 
For a more in depth look—
Joseph Benson’s Commentary of the Old and New Testaments  John 10:1Verily, &c. — The Pharisees supported themselves in their opposition to Christ with this principle, that they were pastors of the church; and that Jesus, having no commission from them, was an intruder and an impostor, and that, therefore, the people were bound in duty to adhere to them against him. In opposition to this, Christ here describes who were the false shepherds and who were the true, leaving them to infer what they were. He introduces his discourse with, Verily, verily, I say unto you — To show, not only the certain truth, but the deep importance of what he uttered. He speaks by way of parable or similitude, taken from the customary way of managing sheep in that country. It is supposed that he was now in the outer court of the temple, near the sheep which were there exposed to sale for sacrifice, the sight of which reminded him of the language of the ancient prophets, “who often compared the teachers of their own time to shepherds, and the people to sheep. Accordingly, in describing the characters of the scribes and Pharisees, he made use of the same metaphor, showing that there are two kinds of evil shepherds, pastors, or teachers; one, who, instead of entering in by the door to lead the flock out and feed it, enter in some other way, with an intention to kill and destroy; another, who, though they may have entered in by the door, feed their flocks with the dispositions of hirelings; for when they see the wolf coming, or any danger approaching, they desert their flocks, because they love themselves only. The Pharisees plainly showed themselves to be of the former character, by excommunicating the man that had been blind, because he would not act contrary to the dictates of his reason and conscience to please them. But though they cast him out of their church, Christ received him into his, which is the true church, the spiritual enclosure, where the sheep go in and out and find pasture.” He that entereth not by the door into the sheep-fold, &c. — “I assure you, that whosoever, in any age of the church, assumed the office of a teacher, without commission from me, and without a sincere regard to the edification and salvation of men’s souls, was a thief and a robber; and in the present age, he is no better who assumes that office without my commission, and particularly without believing on me, and without intending my honour and the good of the church.” — Macknight. Add to this, those do not enter in by Christ, and indeed can have no authority from him, nor ability to become pastors of his flock, who do not first take care to secure, by faith working by love, an interest in, and union with him, or, to be found in him, not having their own righteousness which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith; to be in him new creatures: Philippians 3:9; 2 Corinthians 5:17. But climbeth up some other way — Enters the sheep-fold as a pastor of Christ’s flock, without the necessary prerequisites and qualifications, without first obtaining a saving acquaintance with Christ, and genuine love to him; without being called to, and qualified for the work by him, and of consequence, without authority from him; who, influenced by unworthy motives, by a view to wealth, or honour, or ease, or a maintenance, or some secular employment or advantage, gets himself appointed a minister of Christ’s church, through the interest of rich and powerful friends and connections, or the aid of natural abilities, and mere human learning; or some endowment or accomplishment which is not connected with, and does not imply true piety, and a manifest call from the Lord Jesus; the same is a thief and a robber — In God’s account; entering the fold “to fleece and butcher, not to feed the flock; robbing Christ of his honour, and starving the souls of his people, in order to enrich himself, and aggrandize his family.” — Scott
John 10:2-5. He that entereth in by the door is the shepherd, &c. — “This mode of speaking, with us, conveys the notion that the shepherd is the only person who enters by the door; yet the door-keeper, and the sheep themselves, enter also the same way. The original expression is manifestly intended to denote the constant, not the peculiar, use which the shepherd makes of the door, as opposed to the constant use of thieves and robbers, to force their entrance by breaking or climbing over the fence. The comparison is made, not to the folds used by the common people in remote parts of the country, but to those belonging to the rich in the neighbourhood of a populous city, where the walls and other fences need to be stronger, and the entrance more carefully kept, on account of the greater danger from thieves.” — Campbell. To him the porter openeth — As the shepherd will always choose to enter in by that which is the regular appointed way, so, as soon as he approaches, the door-keeper opens the fold; that is, God in his providence, and by the influence of his Spirit, makes way for such a one to exercise his ministry among his people, and gives success to it. For as it is not unworthy of Christ to be styled the door, by which both the sheep and the true pastors enter, so neither is it unworthy of God the Father to be styled the door-keeper. See Acts 14:27; and Acts 16:14; Colossians 4:3; Revelation 3:8. It was supposed by Sir Isaac Newton, that as the words were spoken near the temple, where sheep were kept in folds to be sold for sacrifices, Christ here alludes to what was peculiar in those folds; that as they were kept locked, they not only excluded the thief, but the shepherd, till the door-keeper opened them. “But I cannot think,” says Dr. Doddridge, “whatever occasion Christ might take from the sight of sheep to represent his people under that image, and himself as a shepherd, he would describe them like sheep shut up in a pen to be sold for sacrifice: nor does the shepherd’s leading them out, &c., agree with this circumstance. In countries where there were so many savage beasts, it might be ordinarily necessary to have the folds better secured than among us; and the chief shepherd might often leave a servant to watch them while thus shut up, and come himself to lead them out to pasture in the morning.” And the sheep hear his voice — The people of God, knowing him to be a true pastor, hearken unto him. All the circumstances here mentioned exactly agree with the customs of the ancient eastern shepherds. They called their sheep by name, went before them, and the sheep followed them. So real Christians hear, attend to, understand, and obey the voice of a shepherd whom Christ hath sent: and he counteth them his own, dearer than any friend or brother; calleth them by name — That is, instructs, advises, directs, encourages each by name, and leadeth them out in the paths of righteousness, beside the waters of comfort. And when he putteth forth his own sheep — Leads them out into the pastures of the ordinances, invites them to the enjoyment of the privileges, and urges them to the practice of the duties of true Christianity; he goeth before them — In all these particulars, and in all the ways of God, teaching them in every point by example, as well as by precept; and the sheep follow him — They tread in his steps; for they know his voice — Having the witness in themselves, that his words are the truth, the wisdom, and the power of God. Reader, art thou a shepherd of souls? Then answer to God: is it thus with thee and thy flock? And a stranger will they not follow — One whom Christ hath not sent, who does not answer the preceding description. Him they will not follow; and who can constrain them to it? But will flee from him — As from the plague. For they know not the voice of strangers — They cannot relish it. It is harsh and grating to them. They find nothing of God therein. In other words, as sheep will not follow a strange shepherd, so the people of God will not hearken to false teachers, or to such as do not declare, plainly, fully, and with a divine unction, the very word of the truth of the gospel: but will avoid them, for they can easily distinguish them from the true messengers of God by their fruits, that is, by their doctrine and practice, and the inefficacy of their preaching to convert, sanctify, and save the souls of men.