One of these stages is to purge the act, whether cordial or formal, form the blemish of acquiring the creatures' pleasure and attracting their hearts for the sake of a praise, and advantage or anything else. And the counterfeit of it is the act performed hypocritically, which is a juristic hypocrisy and is the meanest of all degrees of hypocrisies, and such a hypocrite is the lowest and meanest of all hypocrites.
The second stage is to purge the act from wanting the fulfillment of mundane objectives and transient desires, although these acts may be fulfilled in order to attain to Allah's grace, such as performing night salats [nafilah] for improving one's sustenance, or performing the salat of the first day of the month, for example, in order to be safe from the plights of the month, or giving out alms to ward off diseases, and other worldly objectives. Some jurisprudents [may Allah's mercy be upon them] regard this degree of sincerity to be necessary for the correctness of the acts of worship, in case the objective of performing the act is to attain to it. But this is contrary to investigation according to the juristic rules. Yet, this salat has no value, whatsoever, in the eyes of the people of knowledge, and it is like all other lawful gains, or maybe even lower.
The third stage is to purge the act from trying to attain to corporeal paradises, houris, luxurious abodes and the likes of the corporeal pleasures. Its counterfeit is the worship of the traders, as is described in the noble hadiths. This, too, is, to the people of Allah, similar to other gains, though the wage of the acts of this trader is more and higher, in case he carries them out and rids them from the formal viles.
The fourth stage is to purify the act from being afraid of the threatened bodily punishment and torture. The counterfeit of this is the worship of the slaves, as is mentioned in the narratives.  To the people of the heart, this kind of worship is also of no value and far from being a service to Allah, while, to the people of knowledge, it makes no difference if a man performs an act out of fearing the penalties and punishments of this world or the tortures of the Hereafter, or for the purpose of attaining to worldly women, or for attaining to the paradisiac women, none of them will be for Allah, and they [only] show the intention [reason=da'i] for the performance of an act, which, according to juristic rules, takes the act out of formal invalidity. But in the market of the people of knowledge this stuff is of no value.
The fifth stage is to purge the act from trying to attain to intellectual happiness and everlasting spiritual pleasures, and to join the Cherubim, the group of the sacred intellects and the favourite angels. Its counterfeit is acting for this purpose. Although this stage is great and an important goal, and the wisemen and researchers attach great importance to this stage of happiness and regard it very valuable, yet, in the ways of the people of Allah, this stage has also its shortcomings in suluk, and its salik is also regarded as a trader or a worker, though his trade and business are different, in many ways, from those of others.
As regards this stage, I mean the sixth one, it is to purge the act from being afraid of not attaining to those pleasures and of being deprived of this happiness. Its counterfeit is to act for this stage out of fear. Although this is a lofty stage and is beyond the desire of one like the writer, yet, to the people of Allah, this is also the worship of the slaves, for it has causes.
The seventh stage is to purge it from attaining to the delights of the Divine Beauty and enjoying the pleasures of the lights of limitless glories, which are the Paradise of Meeting [the Lord]. This stage, I mean the stage of Meeting Allah, is one of the most important goals of the people of knowledge and those of heart, and the hands of the hopes of the common people are too short to reach it. Only a few of the people of knowledge are favoured with the happiness of this honour. And the people of love and attraction are of the perfect ones among the people of Allah and His chosen ones. Yet, this perfection is not the most perfect degree of the people of Allah. It is one of their many common states. What we read in some invocations, such as the Sha'baniyah supplication, that Imam 'Ali (AS) and his pure progeny demand the said state, or allude to their being in that state, does not mean that their states are limited to this one, since the eighth stage, which is on the same level as this one, and which is purging the act from the fear of separation, is also not of the perfect states of the perfect ones. Imam 'Ali's saying: "How could I forbear separating from You?"  is just a reference to a brim-full common state of him and of one like him.
Generally speaking, purging the act from these two stages is also a must to the people of Allah, for to act with them will be endued with causes and not free from selfish wants. It is, thus, perfect sincerity. Next, there are other stages which are out of the limits of sincerity, and fall under the criterion of monotheism, abstraction and guardianship, all of which do not fit here.
. As in Wasa'ilush-Shi`ah, vol. 1, p. 45, chs. on "The Preliminaries to the Acts of Worship", the narratives of chapter 9. Usulul Kafi, vol. 3, p. 131, "Book of Faith and Disbeliever', ch. on "Worship", narrative No. 5.
. Misbahul Mutahajjid, p. 778 (Kumayl's invocation)
source : Adabus Salat The Disciplines of the Prayer by Imam Khomeini