Explain the parable of the gardener.

One version is that which was developed by Antony Flew. The idea/essence of the story is as follows: Imagine two explorers come across a clearing in a forest (or wherever they are exploring), and they come across a sort of garden, a clearing where there are both pretty flowers and also weeds growing. One explorer says to the other, "There must be a gardener because there are flowers growing." The second explorer doesn't believe this because a good gardener would remove the weeds from the area. But he is willing to test this, so they sit down and wait for the gardener who doesn't turn up. The first explorer thinks that maybe they just keep looking away when the gardener arrives, so they set a number of traps, perhaps even a net to catch the particularly evasive gardener, and a number of other clever systems. Each time a new trap is installed the gardener is not seen. So is there a gardener?
Well the first explorer's answer is that the gardener is first evasive, but then when they couldn't possibly have missed the gardener (due to a big net, for example), the explorer then takes more qualities away from the gardener and says that the gardener is now silent, then invisible, and undetectable. The main point of the parable is that the second explorer then replies, "What's the difference between that (an invisible gardener) and no gardener at all?" This is of course an analogy which is meant to be compared to God, and how some people say that God can't be detected and so perhaps they are just guessing rather than knowing with any evidence that God exists. Of course there are many arguments against this problem, which lots of religious people find satisfactory.