1)
Why does he ask that his Nefesh not die with sinners?
1.
Radak: Since I chose the company of Tzadikim, I should not die the death of sinners and Resha'im. Their Nefesh is "like water that spilled on the ground, which cannot be gathered" (Shmuel II, 14:14). My Nefesh will be gathered to Your honor when I die!
2.
Malbim: My spiritual Nefesh should not go to Gehinom like sinners' souls, nor should I die like murderers, before their time; so is proper for them.
