One of the most basic concepts of Judaism, is the need and desire to feel Hashem close to us. If we feel this closeness, we feel His constant protection, and we gain peace of mind.
In Parshat Re’eh, this point is made very clearly. G-d places before us, a blessing and a curse. The blessing comes, when we fulfill His commands. The curse comes, when we do not listen to the word of G-d.
Another way of expressing this idea, is also very basic. When we perform a Mitzva, especially one that required a great deal of effort and will power, we are brought closer to G-d. When we transgress the Torah, because of our haughtiness or weakness, the result is that we become more distant from Him.
This is why the Rabbis say that the reward for a Mitzva, is the Mitzva itself. And the punishment for an Aveira, transgression, is the Aveira itself. This is because these actions either bring us closer to G-d, or farther away.
If we read תהילים, the Book of Psalms, we see how much King David longed for this closeness. He said that there is one thing he asked. That is, to dwell in the House of G-d, all the days of his life.
It is the way of the Mussar books to state the obvious. Human nature often allows us to overlook the obvious. Closeness to G-d, is a very strong need for every Jew. The performance of Mitzvot, is the vehicle that will get us there.