Rabbi Yitzchak begins with: "The king joys in Your strength, Hashem, and in Your salvation how greatly he rejoices. You have given him his heart's desire... He asked life of You..." and tells us that David sang this in praise. 'Strength' is the joy of studying the Torah, and 'the king' refers to God. In "He asked life of You, and You did give it him; length of days for ever and ever," we learn that King David only lived 72 years, and that these years were actually taken from Adam, who had a thousand years but only used nine hundred and thirty. Lastly Rabbi Yitzchak talks about the time when the Temple will be rebuilt again in the future.