Why does it mention "Shivti v'Kumi"?
Radak: It mentions man's motions - sitting and standing 1 . Man does as he desires. When he sits and wants to stand, he thinks in his heart why he wants to stand, and vice-versa. Hashem knows man's desires and thoughts.
Malbim: There are four kinds of actions of man. (a) Willful actions that he does without choice. Also refer to 139:2:2:2, 139:3:1:5, 139:3:2:5.
Radak (3): Verse 3 mentions going and lying. One always goes from one of these four to another.
What is the meaning of "Bantah Lere'i me'Rachok"?
Rashi: You understood from afar to draw me to Your will and desire. "Lere'i" is to draw me close to You.
Radak, Malbim: Hashem knows man's thoughts even before he thinks them. "Lere'i" is my thoughts, like "uv'Rayon Libo" (Koheles 2:22). Malbim - this refers to actions done amidst choice of the intellect.
