What should they taste?
Rashi: His word. Radak - knowledge is called Ta'am, e.g. "Ta'amah Ki Tov Sachrah" (Mishlei 31:18). This is like one who tastes a food and tests if it is bitter, sweet, salty or tasteless.
Malbim: Salvation via natural means or people only brings what is pleasant or useful, but not intrinsically good. Hashem is pleasant to the taste ("Ta'amu") and one sees that He is beneficial (u'Re'u), and He is also good.
How should they see?
Radak #1: They should 'see' via intellect.
Radak #2: See with your eyes.
In what way is Hashem Tov?
Radak: Those who take refuge in Him receive good.
Why is one who takes refuge in Hashem happy?
Malbim: Via relying on Him, he receives spiritual happiness of the Nefesh, aside from the benefit of trusting in Him.
