Why did he say "Na'ar", and in verse 22, Elem?
Kli Yakar #1: If I say "Elem", it means that the matter must be Ne'elam (hidden, for he wants to kill you).
Kli Yakar #2: If there is no danger, I can take a Na'ar; this can refer even to an adult, e.g. Yehoshua 1 . If there is danger, I must take an Elem (youth) who will not understand. Indeed, he took a "Na'ar Katan" (verse 35).
Malbim (21, 22): There were two Simanim. (a) Henah means to come, and Hal'ah means to flee. (b) Elem refers to more strength and speed than Na'ar. If I call him a Na'ar, you need not invigorate yourself to flee, rather, reveal yourself where the youth is. If I call him an Elem, invigorate yourself to flee, and do not reveal yourself where the youth is. I mentioned (refer to 20:7:3:1) that there are four possibilities. If I find out that there is no danger, I will give both Simanim to come. If he Vadai wants to kill you, I will give both Simanim to flee. In a case of Safek, I will give one Siman of each.
He was called a Na'ar when he was 42 or 56. Refer to Shemos 33:11:6:1, 33:11:6:1*.
What should David take?
Radak: He should take the youth [and come]. 1
Radak citing his father: He should 'take' (interpret) the Siman, [and come].
Metzudas David: (In this case I will shoot one arrow closer to you than to the youth.) Take the arrow 2 and come.
Why does he need to take the youth? The youth will return by himself! (PF)
Rashi implies like this. Why did he stipulate to take the arrow? Perhaps it is an excuse for David to come to Yehonason (I found your arrow), without exposing that David was hiding and waiting to hear from Yehonason. (PF)
Why did he say "Ein Davar Chai Hashem"?
Radak: There is nothing bad 1 , like Yonason translates. This is because Sha'ul swore "Chai Hashem [Lo Yamus]" - 19:6]. I will say so only if I see that he does not want to harm you.
Our texts of Rashi say 'even if I heard bad from father.' Perhaps this means, 'even if in the past I heard bad
Why did he need a Siman if Sha'ul does not want to harm him? He can tell him overtly, even through a Shali'ach!
Metzudas David: He did not want others to know that he counseled David to hide. 1
