Harei at mikudeshat li
With the words "Harei at mikudeshat li" a man and woman get married. What does that mean? the husband is saying that his wife is holy to him, separate, kadosh, special. She is exclusively his. And he of course becomes exclusively hers.
And when we do a mitzvah, the wording is similar. "Baruch Atah Ado-nai Elo-henu Melech haolam asher kidishanu....." we basically say to Hashem Blessed is He who has sanctified us with his commandments....
So by doing Hashem's will, by doing His mitzvot, we basically are marrying Hashem. We, the Jewish people, are Hashem's bride. We are sanctified and connected to Him through His Torah and mitzvot. And that is a beautiful concept. This is a marriage that is constant, that is renewed every moment. When Moshiach comes our marriage with Hashem will be perfected. But at least now whenever we do a mitzvah we can ponder on how special we are to Hashem and how special and precious every mitzvah is. It is such a privilege to be a Jew. Ashreinu ma tov chelkenu! May we rejoice in our portion and appreciate the fact that we are part of the Jewish nation. May we appreciate that we have a G-dly soul, a part of G-d , within us. And may we feel that sense of responsibility, separating ourselves from all other interests just as a wife separates herself from all other men and becomes exclusively for her husband. Same way we become exclusively for Hashem and reject any subtle form of idolatry or impurity. We need to remember we are sanctified to Hashem, we are holy, pure and we should look up to that idea and give ourselves fully to this Divine marriage.