Why does it say "Ki"?
Radak #1: The following explains why he prayed for Mashi'ach and Binyan ha'Bayis to come soon.
Radak #2: The following explains why "Nichsefah v'Gam Kalsah Nafshi" (verse 3).
Malbim: He explains why he yearns for the Mikdash.
Why does it say "Tov Yom ba'Chatzerecha me'Alef"?
Shabbos 30a: Hashem did not want David to die early, so that his son would build the Beis ha'Mikdash ear;ier. He prefers a day that David engages in Torah to 1,000 Olos that Shlomo will offer!
Rashi: It is better to live one day in Your Chatzeros, and to die the next day, than to live 1,000 years elsewhere (Radak - in a foreign land).
Malbim: The happiness attained in the Mikdash exceeds success that depends on time, and success that depends on place. Regarding time, one day in Your Chatzeros is better than 1,000 days [elsewhere]. Also refer to 84:11:3:
What is the meaning of "Bacharti Histofef mi'Dor b'Ahalei Resha"?
Rashi: I chose to frequent the Saf (threshold) and doorposts [of Beis Hashem] over living in serenity in the tents of Esav ha'Rasha, to cling to them.
Radak #1: I chose to enter the threshold of the gate of Beis Hashem alone, rather than living in a complete dwelling in the lands of the Goyim, which are tents of evil.
Radak #2: "Resha" is like "Lo Yemaket Resha Es Be'alav" (Koheles 8:8), "uv'Chol Asher Yifneh Yarshi'a" (Shmuel I, 14:47), i.e. zeal, overpowering and victory. I.e. I prefer to dwell in the threshold of the gate of Elokim to engage in Chachmah, to dwelling in tents of engagement in this world and zeal for it.
Malbim: Regarding place, I prefer to frequent the threshold of Elokim - the lowliest part of it, than to dwell in a fixed manner in tents of evil, even though they are secure mansions.
