The Jew is commanded to follow rigorous laws, as outlined in tremendous length in the Shulchan Aruch. Much of his time and energies go to fulfilling these obligations.
However, this is only the beginning. There is more to Judaism than “the letter of the law”; the Jew should also strive whenever possible to go “beyond the letter of the law.”
In particular, Pirkei Avos is said to teach mili d’chasidusa, guidelines for pious conduct beyond the measure of the law. We see here from a classical source that that the term chossid refers to the pious one. Similarly, a chossid in the sense of one who follows the path of Chassidus originated by the Baal Shem Tov should behave in a manner of piety.
Granted, even amongst the pious there are many levels of piety, and for various legitimate personal reasons one may choose not to adopt certain hiddurim and chumros, pious practices. It is also necessary to take into consideration that we live in a spiritually low generation in which certain practices may be inapplicable and even damaging for everyone but a select few. Moreover, it is necessary to receive senior guidance in order to discern between pious practices that are personally appropriate and those that are not.
Nevertheless, the chossid’s observance should be inclined in this general direction. For him the law is not a maximum, but a minimum.
Why? Because Chassidus comes to infuse one’s divine service with warmth and passion, with meaning and inspiration.
In a word, love.
Love of the One Who gives us everything we have, Who chose us and showered us with Torah and Mitzvos. Who pulled us out of the depths of Egyptian depravity and raised us to the most sublime heights by giving us the Torah. Our Father, our Husband, our Lover.
One who feels love does not make calculations before displaying affection, and deliberate whether the gesture he desires to express is technically obligatory. And if he would, it would demonstrate that there is a definite lack of love in the relationship.
A chossid is someone in a deep relationship with G–d. He loves Him. And even if he doesn’t yet love Him as much as he should, he genuinely wants to. Reaching this deep relationship is the deepest, most personal goal of his life.
So not only does he not violate G–d’s will, he does even more than G–d asks of him. He is not seeking to follow a rulebook, but to serve G–d with every fiber of his being. Indeed, G–d prescribed rules; however, G–d did not define adhering to the rulebook as the sum total of our relationship with Him.
Thus, violating the rulebook is out of the question. Now, how do I bring myself to an even deeper bond with G–d? Through customs and pious practices.
This principle can be seen in the numerous pious practices accepted in Chassidic circles. In particular, in the Chabad tradition it can be seen (in no particular order) in the tradition to regularly sing niggunim, soul-stirring melodies of deveikus, deep connection with G–d; in the custom to meditate upon G–d’s greatness in order to arouse one to passionate prayer; and in the profound and soul-rousing Kabbalistic insights taught in the intricate teachings of Chabad Chassidic philosophy.
 See Bava Kamma 30a.
 See Kuntres Inyanah Shel Toras HaChassidus, p. 1.