2 Corinthians 8:11
Now therefore perform the doing of it; that as there was a readiness to will, so there may be a performance also out of that which ye have.
Cross-reference
Proverbs 3:28
Parallel
Proverbs 3:28 warns against delaying generosity when you have means — this wisdom supports Paul's call to finish the collection without procrastination.
1 Corinthians 16:2
Historical context
In 1 Corinthians 16:2, Paul instructed them to set aside money weekly — this earlier command shows they already started, making the call to finish in the main verse urgent.
Exodus 35:5
Parallel
Exodus 35:5 calls for a contribution from a generous heart — this OT appeal for willing giving parallels Paul's urging to complete what was begun with readiness.