The Ancestors and Enemies of Avraham

It is clear from the p’sukim of Parashat Bereishit that Adam, Chava, Kayin, and Hevel all believed in Hashem and in fact had the privilege to engage in discussion with Him, each in his or her own way. Even when they strayed from the proper path, they merited hearing words of rebuke from Hashem, which, along with the harsh words, showed great closeness.
By the time of Adam’s grandson Enosh, there was a spiritual downturn, as the pasuk says "then it was mundane (huchal) to call out in the name of Hashem" (Bereishit 4:26). In fact, Chazal relate to Enosh’s generation as the epitome of idol worship (Shabbat 118b). The Rambam (Avoda Zara 1:1) explains the seeds of deterioration, as the people first showed respect to celestial bodies as important agents of Hashem, and then came to increasingly attribute independent powers to them.
In the slippery slope of heresy, the next major jump was to the time of Nimrod. He turned himself into an idol, built the Tower of Bavel as a rebellion, and commanded all to bow down to him. Yeshaya (14:13-14) describes him as one who declared that he would go up to the heavens, above the stars, and be similar to the divine.
The Torah was cryptic in regard to Nimrod, just referring to him as one who "began (hechel) to be a brave man in the land" (Berieshit 10:8). Chazal, based on the hint of huchal-hechel explained that Nimrod "knew his Master and intended to rebel (limrod) against Him," as indeed the name Nimrod indicates (Midrash Aggada, Noach 10).
Avraham Avinu was the only one who dared to stand up to Nimrod. He gathered people publicly and taught monotheism, imploring his followers to follow a good and straight path. He refused to give up his belief even when Nimrod threatened him with being thrown into the fire. The Torah is cryptic about this episode as well, mentioning only the death of Avraham’s brother Haran, "before his father Terach in Ur Kasdim," from which Avraham left (see Bereishit 11:28). The midrash fills in on the dialogue between Nimrod and Avraham, with the former saying that he worships only fire and dares Avraham’s G-d to save Avraham from the fire (Bereishit Rabba 38).
Avraham was saved miraculously from the fire and left Ur Kasdim to go to the Land of Canaan. He continued, with his wife, Sarah, to teach belief in one G-d and called out in the name of Hashem. This was different from Adam who called names … for the animals (Bereishit 2:20).
Surprisingly, Nimrod reappears in the Torah, at the head of a fearsome army of the four kings who defeated the five. In that context, he is called Amrafel, alluding to the fact that through his command, Avraham fell into the furnace. There is even a dispute within Chazal (Eruvin 53a) which of his names was the original one, and which was changed to hint at the element of his persona. In any case, by defeating the four kings, Avraham was able to strengthen the forces of Malkitzedek, the King of Shalem.
As we approach the full liberation, we will experience the nations being "called to the mountain" (Devarim 33:19). The midrash (Sifrei, Zot Haberacha 354) tells how nations will come to Eretz Yisrael for commercial purposes and, while here, will notice and be impressed by the service of one G-d that exists here. They will desire to cling to this wise nation and will convert and offer sacrifices, as the pasuk finishes, "there they will offer sacrifices of righteousness."