Adam Clarke's Commentary on the Bible

Verse 9 (Matthew 7:9)

Or what man is there - whom if his son - Men are exhorted to come unto God, with the persuasion that he is a most gracious and compassionate Parent, who possesses all heavenly and earthly good, knows what is necessary for each of his creatures, and is infinitely ready to communicate that which they need most.

Will he give him a stone? - Will he not readily give him bread if he have it? This was a proverb in other countries; a benefit grudgingly given by an avaricious man is called by Seneca, panem lapidosum , stony bread. Hence that saying in Plautus: Altera manu, fert lapidem, panem ostentat altera . - In one hand he brings a stone, and stretches out bread in the other.

- Adam Clarke's Commentary on the Bible