"Enterprise" begins with the description of a worthy journey. The pilgrims are filled with a sense of purpose and optimism.
It started as a pilgrimage,
Exalting minds and all making
The burdens light.
The pilgrims persevered through the second stage. But, they lose their best writer after disagreeing on the best way to go. They are attacked twice and then a section of the group departs. By this point, they had lost their way and forgotten the purpose and optimism of the journey. They even ceased trying to remember or understand why they were making the journey. "We noticed nothing as we went." Reaching the destination, they determine it had been pointless. Not to mention, the journey was "rare." It had been done before so it's not even original.
The poem is ironic. Having started the journey with great hopes only to end in disappointment, this is an ironic twist in that the grass is not always greener somewhere else. The implication is that if you cannot find inspiration ("grace") at home, you will not find it somewhere else. In other words, grace is not in some particular place; it is found in the individual. Lastly, it is more likely that one will find grace at "home" because this is where one is surrounded by friends and family, and home is where one is more familiar with the significance of natural, cultural, and spiritual symbols, and is therefore more likely to notice grace and thunder.