The Secrets and the Cordial Disciplines of the Four Tasbihs
The Four Tasbihat Recited in the Third and Fourth Rak`ats of the Salat and Their Cordial Secrets and Disciplines as Is Suitable
There are four rukns (pillars) in the Tasbihat:
The first rukn concerns the tasbih (glorification), which is purifying Allah from descriptions by tahmid (saying: al-hamdu lillah = praise is for Allah) and tahlil (saying : la ilaha illallah = there is no god but Allah), which is of the inclusive states. The salik servant should, in all his worshippings, pay attention to that, and prevent his heart from the claim of describing and seeking a eulogy on the Haqq (Allah). He should not think that a servant is able to offer the due servitude to Allah, let alone paying the due homage to the Lord, which is not hoped for even by the perfect walis [auliya'), and from reaching which the hands of the great ones of the people of knowledge are short:
No one can net the phoenix, so undo the net,
Since there can be nothing but wind in it, 
That is why it has been said that the perfect knowledge of the people of knowledge is their knowing their own inability. 
Yes, it is because of the vast mercy of Allah, the Exalted, which covers us, the weak servants, that He vests us, the helpless, with serving Him and permits us to enter into such a holy and pure state which bent the backs of even the Cherubium to get near it. This is of the greatest favours and graces of the Holy Essence, The Provider, that bestowed upon His servants. The people of knowledge , the perfect walis [auliya] and the godly men value it in proportion to their personal knowledge. We-the veiled, left short of all states, the deprived and kept at a distance from any perfection and knowledge-are completely unaware of that, and regard the divine commands, which are, in fact, the highest, big unlimited blessings, as imposition and duty, performing them lazily and with boredom, and that is why we are completely deprived and veiled from its luminosity.
It must be realized that as tahmid and tahlil include Unity of Acts, in which there is the blemish of limiting and decreasing, or even the blemish of assimilation and mixing, the salik servant, to be prepared for entering into it, has to enter first into the strong fortress of glorification and purification, telling his inner heart that Allah, Great and Most High, is innocent of all creational [khalqiyah] individuations [ta`ayyunat] and of the apparels of multiplicities, so that the entering into praising Him can be free from the blemish of multiplication.
The second rukn is tahmid, which is the state of Unity of Acts, suitable for qiyam and recitation. In this respect, these glorifications in the last rak`ats take the place of the surah of al-Hamd, as the musalli is free to recite the surah of al-Hamd (the Openning) instead. The Unity of Acts - as has already been explained in "al-Hamd" - is to be used to exclusively assign praising to Allah, completely cutting short the hand of the servant from praisings. We should convey: "He is the First and the Last and the Outward and the Inward"  to the ears of the heart, and let: "And you threw not when you did, but Allah threw"  reach the taste of our spirit, treading upon selfishness and self-conceit by the foot of behaviour [suluk], in order to take ourselves to the state of tahmid, and out of the burden of being indebted to the creatures.
The third rukn is the tahlil, which is of many states:
One is the state of negating the divinity of act, that is" "There is no effecter in the (world of) existence but Allah", which is a confirmation of confining the tahmid (to Allah) as its cause and factor, because the stages of the possible beings are the shadow of the Real Existence of Allah, Almighty, and mere connection. No one of them, in any way, is independent or self-sustaining. Thus, effecting existence can never be ascribed to them, since effectiveness requires independence in bringing into existence, and being independently effective in bringing into existence necessitates being independent in existing. According to the terms of the people of (gnostic) taste, the reality of the shadow-beings is the appearance of the Power of the Haqq (Allah) in the mirrors of creation. The meaning of la ilaha illallah (There is no god but Allah) is witnessing the Haqq's (Allah's) effectiveness and power upon the creatures, and negating the individuations [ta ayyunatj of creation, and annihilating the state of their activity [fa`iliyat] and their effect in the Haqq (Allah).
The other is the negation of any worshipped other than Allah, and la ilaha illallah means: There is no worshipped except Allah. Therefore, the state of tahlil is the result of the state of tahmid, as when the tahmid is exclusively confined to the Holy Essence of Allah, servitude places its burden in that Holy state, and all the servitudes, which people do to one another for the purpose of being praised, become negated. So, it is as if the salik says that since all praises are exclusively for Allah, servitude must also be exclusively for Allah, Who is to be the worshipped, and all the idols are to be broken to pieces. There are other states for tahlil, which do not suit this situation.
The fourth rukn is the takbir, which also means that Allah is greater than any description. The servant, by commencing the tahmid and the tahlil, denies the description of Allah, and, having finished that, he again denies describing Allah, and glorifies Him, accompanying his tahmid and tahlil with humbleness and confession of shortcomings. Probably the takbir, in this instance, is a takbir of tahmid and tahlil, as they contain the blemish of multiplicity, as has already been said. Probably in tasbih there is tanzih (purification) of takbir and in the takbir there can be takbir of tanzih, where the servant's claims turn to be completely invalid, and he becomes in command of the Unity of Acts, and the state of obeying Allah becomes a habit in his heart, getting out of changing colours into a state of stability.
The salik servant, in these noble recitations, which are the spirit of knowledge, should create in his heart a mood of devotion, supplication, dedication and humility, and by continual repetition give to his inner heart the form of rememberance, fixing the truth of rememberance into his heart such that the heart would be clothed with the clothes of rememberance, taking off its own wear, which is the wear of remoteness [bu'd] (from Allah). Then , the heart becomes divine, truthful, in which will be fulfilled the reality and spirit of:
"Surely Allah has bought from the believers their lives." 
. Poetry from Hafiz Shirazi.
. Biharul Anwar, vol. 94, p. 150, "Supplication Eighteen", "The Supplication of the Gnostics".
. Surah al-Hadid: 3.
. Surah al-Anfa1: 17.
. Surah at-Taubah: 111.
Adabus Salat: The Disciplines of the Prayer
Imam Khomeini (R.A.)