1)
Why does it say "Marbisam Shomerim Mishmeres Beis Sha'ul"?
1.
'Rashi': We should not be astounded why only 3,000 came. Malbim ? most of them were guarding the king (Ish Boshes) and were faithful to him.
2.
Radak: After Avner and Ish Boshes died, these 3,000 came. Until now, they guarded the kingship for Beis Sha'ul, unlike those who came in Sha'ul's lifetime, when David was in Tziklag.
