Why Abraham Was Told Lech Lecha and Kept Every Mitzvah

(Genesis 12:1:) "Now the Lord said unto Abram: Go forth…." Let our master instruct us: What is the rule for a person to take upon himself the Kingdom of Heaven while he is walking? Rav Idi and Rav Huna, in the name of Rabbi Yose bar Yehuda, in the name of Rabbi Shmuel, said: It is forbidden for a person to take upon himself the yoke of the Kingdom of Heaven while he is walking. Rather, let him stand still upon his feet and recite the Shema, and when he reaches "Blessed be the name of His glorious kingdom forever and ever," let him begin "And you shall love"; immediately he may recite it while walking and need not be concerned. You find that whoever is meticulous about the commandments receives much reward. And Abraham was meticulous about the commandments. Rabbi Aha said in the name of Rabbi Alexandri, and Rabbi Shmuel bar Nahmani in the name of Rabbi Yonatan: Even the eruv of cooked dishes was observed in the house of Abraham, as it is said (Genesis 26:5): "Because Abraham obeyed My voice [and kept My charge, My commandments, My statutes, and My laws]." But is there not a single Torah? Rather, this teaches that he was meticulous about every commandment in the Torah. The Holy One, blessed be He, said: You are meticulous about My commandments, yet you dwell among those who serve idols? Go out from among them! From where is this shown? From what they read on the matter (Genesis 12:1): "Now the Lord said unto Abram: Go forth."