For the scripture said, Whoever believes on him shall not be ashamed.…
The word "rich" is here used in its ethical import, as equivalent to liberal or bountiful. Hence the remarkable expression "rich unto." In the sphere of ordinary life, when men become rich, they are in general simply said to be rich — at times it may be said that they are rich in this world's possessions, or that they are rich in the possession of devoted friends, or rich in genius, but God is here represented as "rich unto" — i.e., He is abundant in goodness.
(J. Morison, D.D.)
Parallel VersesKJV: For the scripture saith, Whosoever believeth on him shall not be ashamed.