Praise be to Allah, and peace and blessings be upon the Messenger of Allah. To proceed:
Murāqabah (awareness that Allah is always watching) means that a Muslim constantly remembers that Allah sees him, hears his words, knows his outward and inward states, and is fully aware of his deeds and intentions. Therefore, the believer remains conscious of Allah in both private and public.
Allah, the Exalted, says:
"Indeed, Allah is ever Watchful over you."
(Qur'an 4:1)
He also says:
"And know that Allah knows what is within yourselves, so beware of Him."
(Qur'an 2:235)
The reality of murāqabah is also explained in the famous Hadith of Jibrīl. When he asked the Prophet ﷺ about Iḥsān (spiritual excellence), the Prophet ﷺ replied:
"To worship Allah as though you see Him; and if you do not see Him, then indeed He sees you."
Murāqabah is one of the greatest causes of sincerity, excellence in worship, and avoiding sins. It makes the servant feel modest before his Lord and eager to obey Him in private just as he does in public.
It is also a fruit of believing in Allah's Beautiful Names, such as Ar-Raqīb (The Ever-Watchful), Al-'Alīm (The All-Knowing), As-Samī' (The All-Hearing), and Al-Baṣīr (The All-Seeing). Whoever reflects upon the meanings of these Names will increase in awareness of Allah in both speech and action.
Murāqabah is the constant awareness that Allah is always watching His servant and knows both what is hidden and what is apparent. This awareness leads the Muslim to sincerity, excellence in worship, and avoidance of sin until he attains the level of Iḥsān described by the Prophet ﷺ.
And Allah knows best.