Why did he say "Alecha Nismachti mi'Beten"?
Radak: Even though I did not know, when I left my mother's womb, I relied on You, for You prepared my food via my mother.
Malbim: Not only from my youth - rather, even in my mother's womb, my entire existence is via You.
What do we learn from "mi'Me'ei Imi Atah Gozi"?
Sotah 45b: The initial creation of a fetus is the head - "from my mother's womb, You formed my head." "Gazi Nizrech" (Yirmeyah 7:29) teaches that Gozi refers to the head.
Nidah 30b-31a: Before one is born, an oath is imposed on him. 'You must be a Tzadik... know that Hashem gave to you a Tahor Neshamah. If you will not guard its Taharah, He will take it back.' Gozi refers to an oath - "Gazi Nizrech... " (Yirmeyah 7:29; Nezirus is similar to an oath).
Rashi, Radak: You take me out and move me, like "va'Yagaz Selavim Min ha'Yam" (Bamidbar 11:31). Radak - Gozi is To'ar (i.e. one who takes out); Goz has the same grammatical form as Tov.
Malbim: You cut and detach the fetus from the Me'ayim at the beginning of its formation, and move it to the Beten.
Why did he say "Becha Sehilasi Samid"?
Radak: I always praise myself in You, for the good that You constantly do with me.
Malbim: All my praise was only in You; if You will not save me, there will be Chilul Hashem.
