As the slave is about to conclude his salah, it is prescribed for him to sit down before his Lord, to glorify Him and praise Him with all that befits Him; hence it is dictated for him to proclaim greetings (al-Tahiyyat) which befit Allah alone. It is the custom of kings to have people greet them with different types of greetings, be it in words or actions, as a token of their deference and humility to them. You would find some people praise them by words, some would prostrate to them, some would compliment them, some would supplicate for their kingship to abide forever, and some people would do all the aforementioned; they prostrate to the king, then extol his praises, and then supplicate that his kingship lasts forever. However, as Allah is the true King whose Face is the only everlasting thing while everything else shall come to an end, it befits Him alone to receive the Supreme and Perfect Greetings embodied in al-Tahiyyat. And it is for this reason that some scholars interpreted al-Tahiyyat to refer to His reign while other scholars interpreted it to affirm His everlasting kingship.
The reality is as I have mentioned, it is an all-encompassing greeting that embraces all these aspects: His Reign, Ownership and Sovereignty. All these Attributes are ascribed to Allah (in the most perfect sense) and it befits Him even more because every greeting given to any king, be it a prostration or praise or a supplication for their lasting kinship, in fact, belongs to Allah. That is why the word al-Tahiyyat is prefixed by the definite article (al) that semantically indicates that these greetings encompass all greetings. And the word itself is derived from another word (hayah) that means life; thus it affirms the perpetuity of the greeted. This is similar to how they used to say to their kings: ‘(we hope) you live the life yet to come’, or ‘(we hope) you live ten thousand years’ and so forth. These are the roots of their statements (that we hear to this day): ‘I ask Allah to never cease your days and I ask Allah to lengthen your life,’ and so on and so forth… all these are used to mean continuation and prolongation of one’s life or kingship. For this reason, all such expressions should be used for Allah alone because He is the All-Living, Self-Subsisting and Ever-Lasting One.
Next in these supreme greetings comes the word al-salawat, which affirms the exclusivity of salah to Allah alone. It is for this reason, the word is used in a plural format and structured with the definitive article (al) to assert that anything that can be called salah, be it exclusive or general, is for Allah alone and befits none except Him.
The Wisdom Behind Interlinking al-Tahiyyat and al-Salawat
The wisdom behind interlinking those two words al-Tahiyyat and al-Salawat is that al-Tahiyyat belong to Allah alone as He has ownership of us and al-Salawat belong to Him as we are His slaves, and both of these are entitlements exclusive to Him; greetings are given to Him alone and prayers are intended for Him alone. Then the adjective word al-Tayibat (the good and the pure) is used to qualify His Attributes and His Kingship. It conveys the meaning that He is Good, and so is His Speech, Actions and everything that comes from Him and attributed to Him or associated with His Names. That is to say, His Essence, His actions, His words, and all that he attributed or associated to Himself such as: His House [Muslim no. 2909], His servant [Surah al-Kahf 18:1], His spirit [Surah Maryam 19:17], His camel [Surah al-Shams 91:13] etc are all good.
The meanings of all goodly statements al-Kalima al-Tayyib are His too as they encompass extolling, praising, glorifying and exalting Him with His Attributes and for His Graces such as saying: “You are glorified O Allah and praised! Your Name is Blessed; Your Majesty is Exalted and none has the right to be worshipped save You” and “Glorified is Allah and Praise and thanks be to Allah and there is none worthy of worship save You and Allah is the Greatest” and “There is none worthy of worship save You, Allah is the Greatest, Glorified is Allah and Praise and thanks be to Allah.” and other similar expressions. All good emanates from Him and to Him it belongs; He is Good and accepts nothing but good. He is the Lord and the Ilah of the good; and those who will neighbour Him in the House of honour (i.e. Paradise) are the good ones.
Inner Dimensions of the Prayer by Ibn Qayyim Al-Jawziyyah Pages 58-61