It's rough, getting kicked out of the Garden of Eden, and Herbert uses the language of material hardship to describe it. Adam is created with "wealth and store" but once he makes his fatal error, he loses all of it, going from poor to "most poor." In Herbert's version, Adam is like a careless millionaire who starts out with a great house and pool but after making unwise investments falls into foreclosure and bankruptcy. Talk about a recession.
But the word "decaying"—a surprising choice that doesn't fit in with the other images of material wealth—signals that this poverty might also be a little less literal. Just take the Garden of Eden, which is both physically abundant as well as symbolic of God's abundant love. In the same way, Adam's loss of his material goods = the loss of his spiritual closeness to God. Both types of poverty are made visual in the length of line 5, which clocks in at just two iambs.