Why did he say "Pene Elai"?
Radak: This is like one who turns from his affairs and puts his eyes on one matter.
Malbim: Refer to 86:15:1:2.
Why did he call himself "Ben Amasecha"?
Rashi: He lowered himself in front of his Master more than a slave bought for money. Ben ha'Amah was born in the house, and grew up in his master's family.
Radak: He mentions the mother, for she is the primary formation of the son. And so he said "Ani Avdecha Ben Amasecha" (116:16), for the fetus grows in the mother's womb. He grows and is formed there for the set time. Also after he leaves, he is fed from his mother's milk. Therefore, the son's nature is tied to his mother's more than to his father's. This is why it says regarding Malchei Yisrael "the name of his mother", for the son's acts are usually like his mother's. Even though man has choice, and his deeds are based on how he conducts himself and his habits, part is due to the nature of his formation. I am Avdecha in two aspects - I accustomed myself to Your Avodah, and it is in my nature, for my mother was Your slave.
Malbim: Refer to 86:15:3:2.
