How did a ram suddenly appear out of nowhere? What made Avraham realize that it was there for him to sacrifice in place of Yitzchak?
Rashi and Targum Yonasan: The ram had actually been there since the six days of Creation, 1 but Avraham only noticed it the moment the angel stopped him from Shechting Yitzchak. In fact, Rashi explains that the ram was running towards Avraham, and the Satan caused its horns to become entangled 2 in the thicket.
Rashbam: One minute Avraham saw the ram walking past, then afterwards, 3 it was caught in the thicket. So is must have been the angel that caught it, for him to bring instead of Yitzchak.
Seforno: Avraham realized that the ram was there miraculously, since one moment it was not there, and the next moment it was. 4
See Pirkei Avos (5:9). Gur Aryeh - Why expound in this way? The word "v'Hinei" implies something that had been prepared in advance. Since we do not know when this ram was readied for this task, Rashi explains that it had been ready since Creation.
The word "ba'Sevach" actually has connotations of being entangled. Also refer to 22:13:1.3:1.
This is how the Rashbam translates the word "Achar."
The Seforno adds that this also explains why Avraham was not worried that the ram was privately owned, and that Shechting it would constitute theft.
Had the Torah written that Avraham brought the ram as an Olah, we would have understood that he did it to make up for the missing Olah, So why does the Torah see fit to add "in place of his son"?
Rashi: To teach us how, at every stage of the Avodah, he declared 'May it be considered as if Yitzchak was Shechted... as if blood was sprinkled... as if his skin was flayed... as if he was burned and turned into ashes!'
Why does it say that it was "Ne'echaz ba'Sevach b'Karnav"?
Da'as Zekenim, from Pesikta: HaSh-m hinted that if Yisrael will be caught in Aveiros, they will blow horns (Shofaros) and HaSh-m will recall the Akeidah and vindicate them in judgment.
QUESTIONS ON RASHI
Rashi writes: "It was prepared for this [purpose] since the six days of Creation." Why?
Maharal (Chidushei Agados Vol. 1, p. 106, to Rosh Hashanah 16a): Yitzchak was fit to be an offering, and this ram was to serve as his substitute (Temurah); therefore it also had to have distinguished origin. 1
Maharal (Derech Chayim 5:6, p. 232) writes at length about the items created at twilight of the sixth day of Creation.
Rashi writes: "... Since the six days of Creation." Did this ram really live so long (2185 years)?
Maharal (Derech Chayim 5:6, p. 239): At the sixth day of Creation, it was decreed that it would come into being in the future. [It did not emerge into actuality at that time.]
Rashi writes: "... The Accuser entangled and concealed it among the trees." How is this derived?
Gur Aryeh: Rather than 'was tangled' (Achuz) in past tense, the verse writes "became entangled" (Ne'echaz) in the passive, i.e. it was tangled up by someone else. Rashi explains that it was by the Accuser.
