Why did Hashem decree a famine?
Rashi: In order to exile them to Egypt.
Why does it say "va'Yikra"?
Radak: It is as if Hashem called to the famine, and it came to the land. The decrees that came to the land were from Him. Also Elisha said "Ki Kara Hashem la'Ra'av v'Gam Ba El ha'Aretz Sheva Shanim" (Melachim II, 8:1).
What is "Mateh Lechem"?
Radak: This is like Mish'an Lechem - the food that a person relies on.
This Mizmor discusses Hashem's Chesed. Was the famine amidst Chesed?
Malbim: Yes. Yisrael needed to descend to the iron smelting pot to refine them via affliction. Avraham said "ba'Meh Eda" (Bereishis 15:8), and Hashem answered "Ger Yihyeh Zar'acha" (ibid., 13). Galus Mitzrayim was a preparation to inherit the land.
