As human beings we are always looking outwards for inspiration. The film shows the main characters source of inspiration be the search for intelligent alien life. It's mentioned that the the father, Clifford, may have been trying to escape earth and his family by going on his search, and the space agency says that he may be hiding from them. Clifford is on the extreme end of "looking outwards for inspiration."
Then we have Roy. Throughout the movie and through Roy, we learn that constructive inspiration comes from within. Roy starts off feeling empty and longing for something greater. We see how this dismantles his relationship, how it drives him to look out to the stars.
When finding his father, Roy sees himself within Clifford. They have both endured long periods of time alone, with their mind set on their mission and accomplishing it by any means. He tries to bring his dad back, so to avoid murdering him, and when Clifford is reluctant he tells him "we're all we've got." This is where the film turns toward it's message.
Now throughout the film we are shown bits and pieces of humanity - like the space elevator, the rocket ports, the base on the moon with an Applebee's and other earthly commodity shops. It's mentioned that Clifford would have hated to see the moon like that, just a repeat of earth. Someone says something along the lines of, "we're planet destroyers." So, it's clear that Clifford has a general distain for humanity, thinking lowly of them, in fact so lowly that he remorselessly murders his entire crew to avoid going back to earth. Don't forget that this whole time on the moon were told that humans are actively at war, another huge problem we have with each other.
Now, I will argue that the message of the film is that we need to take a step back and realize that WE are the intelligent alien life that Clifford is out there trying to find. I mean obviously, but we take each other for granted. We are so used to our ways that we think there is no hope for us. We need to take that same inspiration we have for intelligent alien life and have it for one another. We need to treat each other like we would treat some alien race, we should be fascinated and driven by ourselves.
This really is all solidified for me when Roy comes crashing back down to Earth. At this point, we've spent so much of the film in space Earth is looking VERY alien as we see Roy's pod come crashing into the atmosphere. He's been alone for so long on his journey back, he's withered, landing in this unfamiliar place. The hatch opens and BOOM THERE'S THE ALIENS only it's US... HUMANS. In that moment you see these happy, helpful, sentient beings greet Roy and help carry him off.
After this emotional journey that Roy goes on, which represents the viewers journey, Roy starts small with his new inspiration and focuses on what's important, mending relationships. He's only working on fixing one little thing, but it is the reason why that counts. It really provides an interesting perspective on our species that I don't think any film before this has.
TLDR: The movie is trying to show us humans that we need to take a step back and realize what we actually are. Aliens living on a strange remote planet in million to one odds. We should find inspiration and appreciation in this and not continue to exist taking it for granted, rooted in our habitual ways.