13.39 – God blots out whatever He pleases, and He confirms (whatever He pleases)
This verse states literally that Allah erases ( maḥā ) what he wants. As such, it seems to fit in with a series of verses that say Allah cancels (2.106, 22.52) or exchanges (16.101) material in the Quran. For an explanation of the Islamic theory of abrogation, see the comments at 16.101.

13.39 – With Him is the mother of the Book
The expression “mother of the Book” appears here and at 3.7 and 43.4. It seems to refer to a concept of an original book in heaven from which all revelation comes. See the discussion of the “doctrine of scripture” within the Quran at 85.21–22.