Does it mean "keep a pledge/promise". Or it means "stand beside the pledge"? If so ,it might be something like a metaphor..
The Merriam-Webster has three meanings for stand by:
1: to be or remain loyal or true to
I stand by my promise.
He stood by a friend.
2: to be present
We stood by and watched the fight.
3: to be or get ready to act
I'll stand by to help.
Since plegde is very similar to promise, the first sense fits best. So your guess expressed in
Does it mean "keep a pledge/promise"?