Radak: David said so about himself. He said so amidst these [Shir] ha'Ma'alos that are about Galus. Just like he conducted, so Yisrael conducted with lowliness in Galus. Via this, Hashem will have mercy on them - "Ki Ram Hashem v'Shafal Yir'eh" (138:6). Therefore, the Mizmor ends "Yachel Yisrael El Hashem" (3).

Malbim: It discusses how he relies on Hashem in all his matters.

Rashi: I did not conduct with authority. I did not do great matters - pleasures, building and plantings, like my son did. I am in front of You like one without hands and legs - like a formless mass in front of You.

Radak: My heart was not haughty covertly.

Radak (2, citing Yerushalmi Sanhedrin 2:4): My heart was not haughty when Shmuel anointed me to be king.

Malbim: Haughtiness of heart is passing the limit of his desire - in quantity or quality. E.g. one who wants to be an angel, he passes the limit in quality. One who wants to have exceptional strength, he passes the limit in quantity.

Radak: I was not haughty outwardly.

Radak (2, citing Yerushalmi Sanhedrin 2:4): My eyes were not haughty when I killed Galyus.

Malbim: Haughtiness of eyes is passing the limit of intellectual investigation. If he thinks that his understanding is unlimited, and decides with his intellect Divine matters above human intellect, this borders between practical intellect and investigative intellect. The former comes from the heart, and the latter from the eyes, for the foundation of all knowledge is from the senses.

Radak: I did not glorify myself that I understand matters and secrets above my intellect. Rather, I went in them bit by bit, with fear lest I breach to see what my intellect cannot fathom, and it will make me err. "Kevod Elokim Haster Davar", "Devash Matzasa Echol Dayeka" (Mishlei 25:2, 16).

Radak (2, citing Yerushalmi Sanhedrin 2:4): This is when they returned me to kingship, and when I brought the Aron.

Malbim: Also in carrying matters out in practice, I did not go in matters above me - Gedolos in quantity, and Nifla'os in quality.