1)
Why does it say "Chelki Hashem"?
1.
Radak, Malbim: When others chose for their portion money and worldly pleasures, I said that You are my portion. Malbim - "Ani Chelkecha v'Nachalasecha" (Bamidbar 18:20).
2)
What is the meaning of "Lishmor Devarecha"?
1.
Rashi: It is fulfillment of Your words that You made me hope for. Via this, you are "Chelki".
2.
Radak: This is all I have in this world (to guard Your words).
3.
Malbim: This is what I chose - to guard Your words and Mitzvos.
