According to the Gemara (Nedarim 32b), Shem lost his Kohen status due to this verse, in which he blesses Avraham before blessing HaSh-m in the following verse (14:20). This is surprising; did Shem really hold Avraham in greater esteem?
Maharal #1 (Chidushei Agados Vol. 2, p. 12, to Nedarim 32b): A Kohen is a servant of HaSh-m, and his thoughts ought to be directed to Him first and foremost. Shem was found lacking in this regard, and the Kehunah was therefore given to Avraham who fulfilled it.
Maharal #2 (ibid.): Shem recognized HaSh-m though His deeds, (e.g. HaSh-m's aid to Avraham in winning the war). Therefore, Shem mentioned Avraham first, inasmuch as it was the latter's success that led to his appreciation of HaSh-m. But Avraham recognized HaSh-m directly, not just though His deeds. Just as Shem's recognition could come and go due to circumstances, so did his Kehunah. Avraham's awareness of HaSh-m was constant, and so the Kehunah would remain in his family forever. 1
Our Sages describe how Avraham also came to recognize HaSh-m through examining His creations! We must explain that Shem recognized Hash-m when His involvement in world affairs was obvious, but Shem did not succeed in discovering His providence when He concealed his actions. Avraham 's new approach was that the world must have a Director, even at times when He seems to be hiding. Perhaps this is what the Maharal means. (See Maharal, Derush l'Shabbos ha'Gadol, p. 205.) (EK)
"And he blessed him, and said, 'Baruch Avram....'" The verse seems redundant; he blessed after having already blessed him?
Seforno: First Shem blessed Avraham, then he commented that in reality, Avraham did not need his blessing, since he was already blessed by "Kel Elyon" (See Bereishis 12:2).
What is the significance of the term, "Who acquires heaven and earth"?
Rashi: The Pasuk simply means that HaSh-m made heaven and earth, thereby acquiring them.
Seforno: Heaven and earth do not simply exist; they are there by the grace of HaSh-m; they are His acquisitions to do with as He sees fit.
QUESTIONS ON RASHI
Rashi writes: "'Owner (Koneh) of heaven and earth' - ... By creating them, He acquired them to be His." But HaSh-m created everything! Why are heaven and earth singled out as His possessions?
Gur Aryeh: Rashi need not have explained in this way. Chazal teach (Avos 6:10) that heaven and earth are one of the "Kinyanim" of HaSh-m in the world, items that intrinsically belong solely to Him, and are neither matched nor assisted by anything similar.
Maharal (Derech Chayim 6:10, p. 316): The term Kinyan applies only to something under one's full control without any exclusion. (For instance, an Eved is not a generic "Kinyan" to his master, because a master only controls a slave in some respects). Most aspects of Creation do not bring a complete revelation of HaSh-m; rather, only in combination with other creations. Heaven and earth are an example of a Kinyan; 1 they demonstrate HaSh-m's Divinity, and His name is called upon them.
Heaven and earth are counted as one Kinyan, as they are interdependent; see Maharal (ibid).