"And the Lord said to Abram, Go forth (lech lecha)." The numerical value of "lech lecha" amounts to one hundred — a hint to him that when he would be a hundred years old, he would raise up Isaac. Another interpretation of "lech lecha": for to you (lekha) greatness is fitting.
"And the Lord said to Abram, Go forth." What is written above this matter? "And Terah died in Haran." Rabbi Isaac said: According to the reckoning of the count, another sixty-five years are still required, for Terah was seventy years old when he begot Abraham, and Abraham was seventy-five years old when he went out from Haran; thus sixty-five years still remained. Yet it is written, "And Terah died in Haran." Rather, from here you learn that the wicked in their lifetime are called dead. And Abram was afraid that they would profane the name of Heaven through him and would say, "He abandoned his father in the time of his old age and went off." The Holy One, blessed be He, said to him, "Go forth — I exempt you from the honor due to father and mother; and not only that, but I will advance his death before your departure," as it is said, "And Terah died in Haran," and afterward, "And the Lord said to Abram."
With ten trials was Abraham our father tried: (1) Ur of the Chaldees. (2) His being uprooted from his father's house, as it is said, "Go forth." (3) Famine, as it is written, "And there was a famine" (Genesis 12:10). (4) The matter of his wife, as it is written, "And the woman was taken to the house of Pharaoh" (ibid. 12:15). (5) The covenant between the pieces, as it is said, "Know surely" (ibid. 15:13). (6) His wife was barren, as it is said, "And Sarai was barren" (ibid. 11:30). (7) The covenant of circumcision. (8) The matter of Sarah with Abimelech. (9) The matter of the sending away — that he sent away Hagar and her son Ishmael, as it is written, "And the thing was very grievous, etc." (ibid. 21:11). (10) The binding of Isaac.
"From your land, and from your birthplace, and from your father's house [to the land that I will show you]." Why did He say all these to him? In order to give him reward for each and every one.