Adam Clarke on 1 Timothy 5:4

But if any widow have children or nephews - This shows that widows indeed are those that have neither children nor nephews, i.e. no relatives that either will or can help them, or no near relatives alive.

Let them learn first to show piety at home - Let these children and nephews provide for their aged or helpless parents or relatives, and not burden the Church with them while they are able to support them.

And to requite their parents - Και αμοιβας αποδιδοναι τοις προγονοις· Let them learn to give benefit for benefit. Your parents supported and nourished you when you were young and helpless; you ought therefore to support them when they are old and destitute. This is called showing piety; and there is doubtless an allusion to the fifth commandment: Honour thy father and thy mother - provide for them in their old age and afflictions; God commands this.