This points to the worship, humility and submissiveness of the heart to its Lord as perpetual condition wherever it may be: in constant regard (for Allah), whether in solitude or in the company of others.
As salah is built upon five pillars; recitation (qira’a), standing (qiyam), bowing down (ruku), prostration (sujud) and remembrance of Allah (dhikr), it is tacitly called after these actions.
It is called qiyam based on the ayah: “Arise [to pray] the night, except for a little” (Surah al-Muzzammil 73:2) and “Stand before Allah, devoutly obedient.” (Surah al-Baqarah 2:238) and it is called qira’a based on the ayah: “and [also] the Qur’an [i.e. recitation] of dawn. Indeed the recitation of dawn is ever witnessed” (Surah al-Isra 17:78) and “so recite what is easy [for you] of Qur’an” (Surah al-Muzzammil 73:20) and it is called ruku based on the ayah: “and bow with those who bow [in worship and obedience]” (Surah al-Baqarah 2:431) and “And when it is said to them, ‘Bow [in prayer], they do not bow.” (Surah al-Mursalat 77:48) and it is called sujud based on the ayah, “So glorify the praises of thy Lord, and be of those who make prostration (unto Him).” (Surah al-Hijr 15:98) and “But prostrate and draw near [to Allah].” (Surah al-Alaq 96:19) and it is called dhikr based on the ayat: “O you who have believed, when [the adhan] is called for the prayer on the day of Jummuah [Friday], then proceed to the remembrance of Allah” (Surah al-Jummuah 62:9) and “O you who have believed, let not your wealth and your children divert you from the remembrance of Allah.” (Surah al-Munafiqun 63:9).
The most honourable action in salah is prostration and the most honourable dhikr in salah is the recitation of the Qur’an: the first Surah that was revealed to the Prophet, peace and blessings of Allah be upon him, was Surah al-Alaq, whose first ayah is to, “Recite in the name of your Lord who created.” and whose last ayah is to “…prostrate and draw near to Allah”.
Thus the structure of the unit (rakah) in salah is composed accordingly; it starts with recitation and ends with prostration.
Inner Dimensions of the Prayer by Ibn Qayyim Al-Jawziyyah Pages 51-54