Suffering example 1: the speaker says God could explain why the mole "continues blind," meaning why moles have to live without light underground in their tunnels. This sounds unpleasant, right? So why does God doom an animal to eternal darkness? It's almost like being buried alive. The speaker knows God is good, but only God Himself could explain the mole's lot in life.
Why flesh that mirrors Him must some day die, (4)
Suffering example 2: "flesh that mirrors Him" is a reference to human beings. Why, if God made us, do we have to die? Seems unfair and unnecessarily painful. So, what gives, God? Once again, the speaker is citing an example of how, although he knows God is good, he can't understand why we must die. Of course, nobody really knows, and this is an example of the apparent paradox of a good God that requires suffering from His creation.
Make plain the reason tortured Tantalus Is baited by the fickle fruit, declare (5-6)
Suffering example 3: The speaker is referencing Greek mythology. Tantalus was cursed by the gods with never ending hunger, and every time he reaches for a piece of fruit, the fruit moves out of reach. Why is it our desires always leave us wanting more? And nobody knows this better than Tantalus who is always starving but can never be fed. Why, if God is good, would Tantalus continue to desire fruit, which he can never have? Being mere mortals, we can't answer these questions, but the speaker is saying that God could if He wanted to. Of course, God's not making a peep, so this is yet another example of the paradox of God's ways.
If merely brute caprice dooms Sisyphus To struggle up a never-ending stair (7-8)
Suffering example 4: Sisyphus is also from Greek mythology and he's doomed to roll a large boulder up a hill for eternity. The job is difficult, it will never be finished, and life for Sisyphus seems like it'd be totally pointless. This is the last example of suffering in the speaker's list. Of course, there's no answer given from God or the speaker, but the point is that there are things in life that we'll never understand, even really bum deals, like the one Sisyphus got. Just another example of how we don't understand suffering in life.