Ancient Jerusalem was surrounded by a wall. The wall, of course, was meant to keep out the bad guys. But the passage to enter the city was also so small that it was hard for good guys to enter, as well. For a camel to get through it was almost impossible. The loads were removed and the camel had to kneel and scoot through the "eye," as it was called, to get in the city. I hope that gives a visual to an often quoted but not exactly understood reference.
I think this is the second time I have quoted scripture in this blog.
"And again I say unto you, it is easier for a camel to go through the eye of a needle, than for a rich man to enter into the Kingdom of God." Matthew 19:24