To whom did he say "Gadlu la'Shem Iti"?
Radak: He addresses the humble.
For what will they aggrandize Hashem?
Radak: For His salvation of me.
Why did he say "Gadlu" and "u'Neromemah"?
Malbim: Ram is something beyond man's reach - "Shamayim la'Rom". Something Gadol, e.g. a pillar standing on the ground and its head 'reaches Shamayim', everyone perceives it according to his height. The nations considered Hashem to be out of reach, and He does not supervise over them - "Ram Al Kol Goyim Hashem Al ha'Shamayim Kevodo" (113:4). Yisrael consider Him great; everyone relates to Him according to his level. Hashem Himself is Ram; intellect dictates that He would not lower Himself to supervise a lowly creation like man. Experience teaches that He is Gadol; He supervises all His creations, especially Yir'ei Hashem, and hears their prayers. You must admit that He is Gadol! "U'Neromemah Shmo Yachdav" - I agree that His name (essence) is elevated above any understanding.
