It said above (2:18) that he served Hashem. Why was this repeated?
Malbim: The Navi gives six reasons why Hashem chosen to give prophecy to Shmuel then. (a) He was constantly serving Hashem, and in front of (at a higher level than) Eli. 1 (b) Prophecy was rare, because people were not prepared for Ru'ach Hashem to take effect on them. There was Divine desire to bestow influence, and Shmuel was [most] prepared for it. (Refer to 3:2:1:2, 3:2:2:2, 3:2:3:1*, 3:3:3:2 for the other reasons.)
Malbim: This is why it does not say like above (2:11) "Es Pnei Eli."
What is the meaning of "Hayah Yakar"?
Rashi: It was withheld. This is like "Yekar Ru'ach Ish Tevunah" (Mishlei 17:23) - a man of understanding withholds words.
Radak: There were not prophets.
What is the meaning of "Ein Chazon Nifratz"?
Rashi citing Targum Yonasan: It was not revealed (spread), like "u'Faratzta Yamah va'Kedmah" (Bereishis 28:14).
Radak: Prophecy was fenced and sealed.
