The Thief

Joh 10:1  "Truly, truly, I say to you, he who does not enter by the door into the fold of the sheep, but climbs up some other way, he is a thief and a robber.
Joh 10:2  "But he who enters by the door is a shepherd of the sheep.

Joh 10:7  Jesus therefore said to them again, "Truly, truly, I say to you, I am the door of the sheep.
Joh 10:8  "All who came before Me are thieves and robbers, but the sheep did not hear them.

Joh 10:10  "The thief comes only to steal, and kill, and destroy; I came that they might have life, and might have it abundantly.

This isn't about the devil as I've heard so many people claim, but rather this is about illegitimate shepherds, who see themselves as the gatekeepers, those who aren't in Christ and demand others to come to the "truth" through their leadership and their opinions. False teachers seek to destroy the sheep of Christ. The only way to to discern, mark, and then reject such fake leaders is to know, believe, trust, and obey the Word of God, which the Holy Spirit will use  to protect and nurture your spirit and mind.

Isa 8:20  To the law and to the testimony! If they do not speak according to this word, it is because they have no dawn. 

1Jn 4:1  Beloved, do not believe every spirit, but test the spirits to see whether they are from God; because many false prophets have gone out into the world. 

2Co 11:3  But I am afraid, lest as the serpent deceived Eve by his craftiness, your minds should be led astray from the simplicity and purity of devotion to Christ. 
2Co 11:4  For if one comes and preaches another Jesus whom we have not preached, or you receive a different spirit which you have not received, or a different gospel which you have not accepted, you bear this beautifully.

2Ti 3:13  But evil men and impostors will proceed from bad to worse, deceiving and being deceived. 
2Ti 3:14  You, however, continue in the things you have learned and become convinced of, knowing from whom you have learned them;
2Ti 3:15  and that from childhood you have known the sacred writings which are able to give you the wisdom that leads to salvation through faith which is in Christ Jesus.
2Ti 3:16  All Scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness; 
2Ti 3:17  that the man of God may be adequate, equipped for every good work.

2Co 11:13  For such men are false apostles, deceitful workers, disguising themselves as apostles of Christ. 
2Co 11:14  And no wonder, for even Satan disguises himself as an angel of light. 
2Co 11:15  Therefore it is not surprising if his servants also disguise themselves as servants of righteousness; whose end shall be according to their deeds.