What is the meaning of "Gamar"?
Rashi: It is finished (none remain).
Who is "Chasid"?
Malbim: He does a Chesed that he did not promise, and does extra Mitzvos amidst Chasidus (above his obligation).
What is the meaning of "Fasu"?
Rashi: This is like Afsu (ceased). Also Menachem explained so.
Who are "Emunim"?
Malbim: They are people of Emes who fulfill what they promise, and they do the Mitzvos that are obligatory on them.
Why did David say that no faithful people remain?
Rashi: All say Sheker about me, and spy out the places where I hide. They tell "l'Sha'ul ha'Lo David Mistater Imanu" (54:2).
Radak: Most of this generation are Resha'im. They make secret plots against the poor and weak. Therefore, "Hoshi'ah Hashem" (He must save from them)!