Introduction

The salat has been described in some ahadith as "the pillar of religion.
" Imam 'Ali (a.s), after receiving the fatal injury by Ibn Muljim (may Allah curse him), in a part of his advice to his sons, al-Hasan and al-Husayn (a.s) said, "[Fear] Farewell Allah, and keep Allah in view with regardst salat, for it is the pillar of your religion.
[Fear] Allah, and keep Allah in the matter of the house of your Lord (i.e., mosque): do not leave it empty as long as you live." ⁽¹⁾

As-Sukuni narrates from Imam as-Sadiq (a.s), "The Messenger of Allah (s.a.w.) said, 'Satan is frightened from a believer as long as he keeps up salat on time; but when he starts neglecting them, Satan becomes emboldened and tempts him to commit major (sins).
'" ⁽²⁾ Yazid bin Khalifa said that he heard Imam as-Sadiq (a.s) say, "When a person stands for salat, mercy descends upon him from the heaven to the earth and the angels engulf him, and an angel calls out: 'if this person knew what is [the reward] for the salat, he would never stop.'" ⁽³⁾

From these [few selected ahadith] we can understand the clear and obvious importance of salat in Islam.
And since salat is like having audience with the Almighty Allah (as the ahadith have it that a person standing for prayer is as if he is standing in audience of the Almighty), the worshiper should approach Allah through presence of heart by not thinking or occupying his mind with anything worldly and transitory.
Almighty Allah says in the Holy Qur'an: "Indeed successful are the believers who are humble in their prayers.
" (24:1)

When Imam 'Ali Zaynu 'l-'Abideen (a.s) said his salat, he used to stand "firm and motionless like a tree: nothing moves on it except what is moved by the wind." ⁽⁴⁾ When the Imams, al-Baqir and as-Sadiq (a.s), stood for their salat, "their colour would change to red and then yellow as if they were talking to someone whom they could see." ⁽⁵⁾