Mercury has to do with details and Sagittarius is a sense of hope, meaning and purpose.
Mercury in Sagittarius may be too hopeful with information, forming too many black and white conclusions too fast – as they are looking for information to be inspiring, rather that to be correct. Those things are completely different.
And yet the intersection of Mercury and Jupiter ruled signs is conceptually a good one – as we need to connect details with a bigger picture in order for beliefs to be more than Dogma, and information to be more meaningful than just data analysis.
When Mercury is in Sagittarius it brings this mind of details, discrimination and neutrality of Mercury into the realm of Sagittarius, which is about inspiration, beliefs philosophy and a sort of black and white, approach those things.
Sagittarius shows our beliefs which gives our life a direction and a trajectory. With Sagittarius it’s about how these beliefs inspire us toward our goals. It’s like standing at the bottom of the mountain – you see your goal and say “if I get there I’m enlightened”. So we try to keep following the path, but along the way we have these other things that try to derail us. In Sagittarius though, were not going to be derailed because we know the right way to go and we can see the goal.
But of course we get distracted. Mercury in many ways is all those details along the way that may distract us.