Groot is introduced to the viewer with his more vocal friend and business partner Rocket Raccoon, as a typical other-worldly action hero. He has a limited vocabulary, which is often translated by his companion Rocket, but more often than not is understood through his inflection. It is not until the undoubtedly, at least in their own minds, more capable members of the rag-tag group that comprise the Guardians hit a stumbling block that Groot's value to the team is realized.
He doesn't carry a flashy gun, wear the uniform, or buy-in to other such standard fare for action figures, he is the ultimate weapon because of his effect on the morale of his team. One can't help but draw comparisons to how necessary the resources of nature are often undervalued, but ultimately necessary to the morale of humans.
With his large brown eyes, we sense the deep connection he feels for the world around him, especially towards his friends, the Guardians. All of the humanesque members of the Guardians subscribe the the very American concept of the "Me first" mentality, whereas Groot is the first to put the team before himself, and give traction to the ability of the other Guardians to do the same.
Early on, he is seen as relatively useless by the other Guardians, but he isn't much of a talker, so he is tolerated. As with nature, he is often overlooked, his beauty seen as a waste of resources to human eyes. It is in the later moments of the film that really bring together the bond between humans and nature, and leaves the question, what are we without each other? Or, so simply said by the anamorphic tree himself, "We Are Groot."