[nonethewiser]

The point is there is a belief in a consequence for lying to God. Whether or not there is an actual consequence is irrelevant.

Furthermore, you can’t prove what happens after you die. I mean you may very well be right, but it’s just your personal belief.

[SigmundA]

Based on my interpretation of the Pale Blue Dot someone swearing to it would most likely be trying to convey a belief in consequences that occur regardless of the existence of a supreme being.

That is a belief in personal responsibility not motivated by fear of punishment by a supreme being.

This quote from Sagan convey's that meaning among others IMO:

It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.

Also see

https://en.wikipedia.org/wiki/Lawrence_Kohlberg%27s_stages_o...

Where fear of gods punishement would be at the lowest level.