According to Groucho Marx, "Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read."
While that is no doubt true, it is far less life-changing than the outside/inside comparison drawn by Chinese evangelist, Watchman Nee:
"Outside of Christ, I am only a sinner, but in Christ, I am saved. Outside of Christ, I am empty; in Christ, I am full. Outside of Christ, I am weak; in Christ, I am strong. Outside of Christ, I cannot; in Christ, I am more than able. Outside of Christ, I have been defeated; in Christ, I am already victorious. How meaningful are the words, 'in Christ.'"
It reminds me of an old Sunday School song I sang as a child: "One door and only one, and yet its sides are two: Inside and outside; on which side are you?"
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Truth is..."Truly, truly I say to you, I am the door of the sheep. All those who came before Me are thieves and robbers, but the sheep did not listen to them. I am the door; if anyone enters through Me, he will be saved, and will go in and out and find pasture. The thief comes only to steal and kill and destroy; I came so that they would have life, and have it abundantly."
(Jesus - John 10:7-10 NASB)