Why does it say "Ki Yakov Bachar..."?
Radak: You are proper to praise Him more than any nation, for He chose you among all the nations.
Malbim: This explains that also His name, i.e. fixed ordered conduct, is pleasant. Also it has Hashgachah over Yisrael. Even though it depends on causes of the Ma'arachah and Mazal, which do not danger between Tzadik and Rasha, Hashem's nation is different. For them, also nature is under Hashgachah; they are conducted according to merit, evil, Avodah and rebellion.
Why does it say "Yisrael li'Sgulaso"?
Malbim: Yakov refers to the masses. Yisrael refers to the Gedolim, people of spirit, or the entire nation, when they are at a high level due to their deeds. Hashem chose even the former; they are not under the Sarim of the Ma'arachah. Yisrael are a Segulah, something very dear stored in a special storehouse, and He oversees them every moment.