Gardener vs. Gravedigger

I was reading Hamlet, Act V, like Sexson said to, and came across a peculiar line. It was said by Clown 1: "Come, my spade. There is no ancient gentlemen but gardeners, ditchers, and grave makers: they hold up Adam's profession."
I was confused by this line, so I looked it up (or googled it) and found that Adam's profession was a gardener in the garden of Eden. This would make great/logical sense, BUT I kept reading and also found that Adam was demoted from that job after he ate the apple, thus the fall of man, ect. Interesting...I think so. What profession was the Clown referring? Was it simply the gardener or Adam's later duty? Well, in Genesis it quotes: "Therefore the LORD God sent him forth from the garden of Eden, to till the ground from whence he was taken."
In order to better understand this line from Genesis I reread, then read again and found an early passage that helped me understand. "Thorns also and thistles shall it bring forth to thee; and thou shalt eat the herb of the field; 19 In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken: for dust thou art, and unto dust shalt thou return."
Now, we are getting somewhere. I believe, because Shakespeare was a scenic, that the Clown truly means Adam's second profession. God is saying that Adam's new job is to dig graves. If man is born out of dust, or dirt, and we return to that same dirt later on, in our graves. Then Adam must till the ground that he eventually will end up in. This passage by the Clown is very ironic. Adam's profession changes from a preserver and creator of life, such as a gardener. To the "builder of death." Adam's profession is to build houses for the dead because he is ultimately doomed.
Towards the end of the gravedigger's scene, the first Clown asks a riddle. He asks, "Who builds stronger than a mason, a shipwright, or a carpenter?" The answer is a "grave-maker; the houses that he makes last till doomsday." I think this riddle goes back to the comment earlier. And there ends my question on Adam's profession.