What is the meaning of "Terem"?
Rashi: Every Terem in Tanach means 'not yet.' (Shmuel did not yet recognize the voice of prophecy.) It does not mean 'before.' 1
Rashi: Our verse proves this, and also from "Terem Tira'un" (Shemos 9:30) and "Kol Si'ach ha'Sadeh Terem Yihyeh ba'Aretz" (Bereishis 2:5).
Why does it say both "v'Terem Yigaleh Elav" and "Terem Yada Es Hashem"?
Radak #1: Both mean that he had not yet had prophecy from Hashem; this is why he did not understand that Hashem was calling him. The matter is repeated.
Radak #2: Terem Yada means that he had not yet learned Divine Chachmah, even though he learned other Chachmos. Had he learned Divine Chachmah, he would have known that it was a voice of prophecy. 1
Malbim: He had not yet learned how Hashem gives prophecy, and he had not yet experienced prophecy.
Radak says that Targum Yonasan holds like this ('he had not learned to know fear of Hashem'); our text of Yonason is different. (PF)