world's second funniest joke

Sherlock Holmes and Dr. Watson go on a camping trip. After a good dinnerand a bottle of wine, they retire for the night, and go to sleep.
Some hours later, Holmes wakes up and nudges his faithful friend.
“Watson, look up at the sky and tell me what you see.”
“I see millions and millions of stars, Holmes” exclaims Watson.
“And what do you deduce from that?”
Watson ponders for a minute.
[size=18]“Well, astronomically, it tells me that there are millions of galaxies and potentially billions of planets. Astrologically, I observe that Saturn is in Leo. Horologically, I deduce that the time is approximately a quarter past three. Meteorologically, I suspect that we will have a beautiful day tomorrow. Theologically, I can see that God is all powerful, and that we are a small and insignificant part of the universe. What does it tell you, Holmes?”
Holmes is silent for a moment. ‘Watson, you idiot!” he says. “Someone has stolen our tent!”
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chokran 3la lmajhod

nice joke but actually i didn't get the meaning,i didn't lough either!!!!! will you explain it please?!
and thank you anyway!