Why did he say "Yachid v'Oni Ani"?
Rashi: The sin of many depends on me. Compared to them, I am an individual. Therefore, turn to me and grace me. My Tefilah is needed for all Yisrael 1 !
Radak: Even though I am king, and I have a great nation, I do not trust in many troops, only in Your Gevurah. Oni is humble, like "Yechaletz Oni v'Anyo" (Iyov 36:15).
Malbim: Amidst his separation, and clinging to Hashem, he depicts himself as separated from the entire world - his neighbors, friends, household, and also his wealth. Turn to me, for I have nothing in this world!
Radak citing Shocher Tov: David was not Yachid - he was Yishai's seventh son (Divrei ha'Yamim I, 2:15)! He was not poor - "v'Hinei v'Anyi Hachinosi l'Veis Hashem Zahav Kikarim Me'ah Elef" (ibid., 22:14)! Rather, he said 'since You made me king over Your children and their eyes depend on me and all need me, and they are Rabim, and my eyes depend on You, I am an individual compared to them.
