My approach will likely improve over time, but for now it is based on a few main factors.
1) Is the content primarily concerned with teaching the Bible?
2) Does the teaching fall within what is broadly considered orthodox?
3) Is it a good "fit" for the UX of the app?
By "fit" I mostly mean duration. If there is a good sermon, but it's 45 min long, then it may not be approved. Since people are actively reading the Bible, ideally a video will say something meaningful and specific about a Bible passage without taking too long (<5 mins).