1)
When did David say so?
1.
Rashi: He said so in his heart when his youths told him Naval's refusal.
2.
Malbim: He said so now. He saw the youths, and thought that they were going to Naval's house.
2)
What is the meaning of "la'Sheker"?
1.
Radak: It is for naught.
3)
What evil did Naval do to David?
1.
Radak: He verbally reviled him.