While it is true that many people have said many things over the years on this subject, we would do well to go to God's own book and read His own instructions:

"Verily, verily, I say unto you, he that entereth not by the door into the sheepfold but climbeth up some other way, the same is a thief and a robber.  But he that entereth in by the door is the shepherd of the sheep…..Then said Jesus unto them again, Verily I say unto you, I am the door of the sheep.  All that ever came before me are thieves and robbers: but the sheep did not hear them.  I am the door; by me if any man enter in, he shall be saved, and shall go in and out, and find pasture……As the Father knoweth me, even so know I the Father; and I lay down my life for the sheep."  John 10:1, 2, 7-9, 15