1)
Will he speak Hashem's praise only in the future?
1.
Radak: This refers to when he will be revived with the dead.
2.
Malbim: My mouth will speak His praise forever, for His praise has no end,
2)
Why does it say "vi'Yvarech Kol Basar"?
1.
Radak: All people 1 will serve Him together - "Yavo Chol Basar Lehishtachavos Lefanai" (Yeshayah 66:23).
2.
Malbim: Even though they do not understand the praise of Hashem Himself, they will bless His name, which is what is known of Him via the Brachah that we receive from Him (refer to 103:1:4:5).
1
Radak: Similarly, "Hi Haysah Em Kol Chai" (Bereishis 3:20) refers only to people.
