The actions of those morally responsible take one of eight rulings:
1. The Obligatory (fard) is a firm command established by a decisively-established text whose meaning is decisive and not open to the possibility of interpretation.One is bound to believe in and act on the obligatory. The one who denies it could well fall into disbelief, and the one who leaves it is sinful.
2. The Necessary (wajib) is a firm command affirmed by a text that allows the possibility of interpretation.
Denying something necessary is corruption (fisq) but not disbelief. Leaving it is sinful.
The ruling of necessary aspects of the prayer is that the prayer is not invalidated by their omission; however, it becomes necessary to repeat it if they were left out intentionally. If left out forgetfully, a forgetfulness prostration is necessary at the end of the prayer; if this too is left out, then it is necessary (wajib) to repeat the prayer.
3. The Confirmed Sunna (sunna muakkada) is that which our Prophet (Allah bless him and give him peace) or the Companions did most of the time (and was not of worldly habits)
One who leaves it without excuse deserves reproach, not punishment. Leaving it habitually is sinful, though, because it entails turning away from the guidance of the Messenger of Allah (Allah bless him and give him peace), whom we have been commanded to follow.
4. The Recommended (mustahabb) is that which our Prophet (Allah bless him and give him peace) did sometimes.
The one who performs it is rewarded, and one who does not is not worthy of reproach.
5. The Permissible (mubah)entails neither reward nor punishment. Such acts are rewarded, however, if accompanied by a good intention.
6. The Somewhat Disliked (makruh tanzihan) is that which we have been lightly commanded to leave, though it is not sinful or blameworthy to do. There is reward in leaving it.
7. The Prohibitively Disliked (makruh tahriman) is that which we have firmly commanded to leave, through a text open to the possibility of interpretation.
Denying such a command entails misguidance but not disbelief. Performing such an action is sinful.
8. The Forbidden (haram) is that which we have been firmly commanded to leave, through a decisively-established text.
The obligatory and necessary must be performed. The prohibitively disliked and forbidden must be left. It is strongly emphasized to perform the confirmed sunnas, and blameworthy to leave them without excuse. The recommended should be performed, and the somewhat disliked should be left. The permitted should be conjoined with good intentions, to be worthy of reward, and one should avoid wastefulness.
The way of love and slavehood entails doing everything ones Lord commanded, whether firmly or lightly, and avoiding everything ones Lord interdicted, whether firmly or lightly. The way to operationalize this, however, is best through a gradual and steady manner.
 Decisively established texts are the entire Quran, and those hadiths related by multiple contiguous chains (mutawatir).
 Being wasteful in using the permitted is blameworthy and can even become sinful if excessive.
 Abu Hurayra (Allah be pleased with him) related that the Messenger of Allah (Allah bless him and give him peace) said, Verily, this religion is easy, and no one makes their religion excessively difficult except that it overcomes them. So be moderate, do your best, and be of glad tidings [Bukhari (39), Muslim (2816)]
Source: The Absolute Essentials of Islam (Faraz Rabbani, http://www.WhiteThreadPress.com, Fall 2004).
MMVIII © Faraz Rabbani and Qibla.