system
Given the following post, respond as if you're commenting on Reddit:
human
[DC/Warhammer 40K] I've just found a motherbox and have been deemed worthy to use it. What do I do? Should I report it to a Tech Priest? Try to use it? Is it Tech Heresy?
gpt
Let's forego the obvious observation that, as an average Imperial citizen, you'd be a hiveworlder indentured to a manufactorum and worked half to death, with next to no knowledge of how the wider Imperium works and your possibilities within it, because that's boring. Let's assume you're someone with substantial knowledge but not too much starting power, like minor hive nobility.

Let's also say the MotherBox imparts on you thorough knowledge of its powers and enough of them (initially at least) to be protected from most physical and mental assault. Since you're educated hive nobility, you know that's not enough; not unless you've willing to sacrifice everything and everyone in your life. Your personal and dynastic rivals would be more than willing to hold your entire family hostage to get you to play ball. The Inquisition would be happy to throw them into forms of torture not even the MotherBox can properly imagine, if they think it'll be leverage on you. The Imperium as a baseline is a society that spares no cruelty.

So, assuming you don't want to become some outcast star god hunted down by anyone brave and foolish enough to think they can take what you have, I'd say your best bet is to lay very low, and use your newfound powers to plan ahead very carefully. Gather information, hide your tracks, try to find out if there's anyone in a position of high power that can also be trusted not to screw you over, and go to them.

At the moment, in the Era Indomitus, your best overall bet would be to try to reach Guilliman. The guy may be willing to order the death of trillions, but he's not actively malicious. If you go to him, reveal your power, and submit to whatever tests he'll doubtlessly impose to earn his trust, you can probably become a highly placed agent, with you family/friends/allies being granted the highest level of protection as part of the package.