In the Tasawwuf terminology Muraqaba means "to watch over one’s heart or to keep an eye over one’s heart" i.e. to take care of one’s heart & inner self from being corrupted. The Quran gives much importance to this practice and also Prophet Muhammad ﷺ emphasized its importance throughout the 23 years of his prophetic mission.
Our hearts are spiritual centers through which we can keep our individual connection with Allah ﷻ but the Duniya (world and its pleasures) and Nafs (evil commanding soul) attempt to corrupt it. Nafs continues to be tempted by the Duniya and every time we yield towards its temptations we impact our hearts. Allah ﷻ says in the Quran: (Al Quran 26:88–89) "the Day on which neither wealth will be of any use; nor children, [and when] only he [will be happy] who comes before God with a heart free of evil!"
Whoever keeps their heart pure from all dross in this world will come on judgment day with the same purity. The human heart as long as its physically alive is under continuous exposure from all sorts of evil and negative influences especially in times like ours where worldly pleasures are presented to us in a beautiful and deceiving manner. What impacts a child’s upbringing as well as the thought process of adults are the environmental factors, they impact our five physical sense perceptions. The exposure received by our senses results in leaving traces internally on our souls and hearts. For instance whatever we hear and see, as long as its not filtered through God consciousness will impact our inner selves and effect our behavior in the near future or in the long run. Exposure to negativity through what we watch, hear or read has the potential to misguide us in to disbelief (Kufr) and the exact purpose of Muraqaba is to defend one’s internal self from such effects. Prophet Muhammad ﷺ taught us how to maintain Muraqaba by teaching us something called Ihsaan: “Ihsan is to worship Allah as if you see Him, and if you do not achieve this state of devotion, then (take it for granted that) Allah sees you." (Sahih Bukhari)
Maintaining such consciousness that Allah ﷻ watches us keeps us in check and assists us in protecting our inner selves from negative influences. In fact even if the negativity was to impact us and we commit sins due to our weak nature that Allah ﷻ created us with (Al Quran 4:28) we should immediately resort to Him for forgiveness and protection which assists us in maintaining such concentration in long run. The Quran guides us to maintain internal purity: (Al Quran 91:7–10) "...To a happy state shall indeed attain he who causes this [self] to grow in purity, and truly lost is he who buries it [in darkness]." Abu Said Abul Khayr (440 Hijra, C.E. 1048] one of the greatest saint referred to the importance of Muraqaba when asked: "So and so walks on water (without sinking. What do you think)?" He replied, "It is quite easy. Seagulls walk on water, too." They said, "So and so flies in air." He said, "Birds and flies can fly, too." When they said, "So and so goes from one city to another in a flash," his answer was: "The devil also can travel from the far east to the far west in the same breath. Such things are of no value. A manly person will lead a life like anybody else. He will do shopping. He will get married. And he will not forget Allah even for a moment."
Allah ﷻ says: (Al Quran 13:28) "and whose hearts find peace in the remembrance of God- truly it is in the remembrance of God that hearts find peace." The continuous remembrance of Allah ﷻ in our hearts throughout the day in addition to the obligatory act of salaah (5 times prayers) will assist us to experience His presence and our spiritual connection that keeps us on the path of guidance. This is all included in the concept of Muraqaba, it is extremely important and necessary for a believer as long as he or she lives.