What is the meaning of "Al Ken Ahavti"?
Rashi: Because I loved Your Mitzvos, it is proper for You to teach to me the time of Ratzon (approval), and what I will do to be pleasing to You. Often, "Al Ken" means 'because', e.g. "Al Ken Ra'isi Fanecha" (Bereishis 33:10).
Radak: Because I see that they annulled Your Torah, and pursue unjust gain, and all their engagement is to acquire money, therefore I loved Your Mitzvos, to teach them, so they will engage in them more than in acquiring gold.
Malbim: Because I know that there is a time when You will bring Mishpat on everything hidden, I loved Your Mitzvah, for I knew that there is Hashgachah, reward and punishment.
Why does it say "mi'Zahav umi'Paz"?
Radak: Refer to 119:127:1:2.
Malbim: I love Mitzvos more than gold, which helps 1 , but it does not save from Your punishment - "Lo Yo'il Hon b'Yom Evrah u'Tzedakah Tatzil mi'Maves" (Mishlei 11:4).
I.e. one can buy his needs with gold. (PF)
