Praying the salah properly with all it's external and internal etiquettes (proper manners) has been described in the Quran and Hadith as an indicator of true faith in Allah.
Whereas, habitually Praying salah in a careless and spiritually irresponsible manner is considered as a disaster for one's faith and a sign of nifaq (hypocrisy).
"Successful indeed are the believers. Those who offer their Salat (prayers) with all solemnity and full submissiveness. [23:1-2] And those who strictly guard their Salawat (prayers)." [23:9]"So woe to the worshippers Who are neglectful of their prayers, Those who (want but) to be seen (of men)." [107:4-6]
"And seek help in patience and Salaah and truly it is extremely heavy and hard, except for the Khashi'oon (those who are humbly submissive to Allah)."
"Verily, the hypocrites seek to deceive Allah, but it is He Who deceives them. And when they stand up for As-Salat (the prayer), they stand with laziness and to be seen of men, and they do not remember Allah but little." (4:142)
The Prophet ﺻﻟﻰﺍﷲ ﻋﻟﻳﻪ ﻮﺍﻟﺳﻠﻡ said:
2. Abu Musa (ra) reports that one day the Prophet ﺻﻟﻰﺍﷲ ﻋﻟﻳﻪ ﻮﺍﻟﺳﻠﻡ led the Companions in Salah and then sat amongst them. A person then entered and performed Salah. He was very hasty in bowing and prostrating. The Prophet ﺻﻟﻰﺍﷲ ﻋﻟﻳﻪ ﻮﺍﻟﺳﻠﻡ said, “Look at this person. If he were to die, he would not die on the religion of Muhammad ﺻﻟﻰﺍﷲ ﻋﻟﻳﻪ ﻮﺍﻟﺳﻠﻡ. He is pecking at Salah like a crow pecks at blood.” (Sahih Ibn Khuzayma)
3. When a person performs Salah at its earliest (most desired) time, that Salah ascends towards the heavens. It becomes light for the person and subsequently it reaches the Throne and supplicates for the forgiveness of the person who performed Salah until the Day of Judgement. It says, ‘May Allah Ta’ala safeguard you just as you safeguarded me.’ When a person performs Salah after its allocated time has passed, the Salah goes towards the heavens in such a manner that it is covered in darkness. When it reaches the Throne it is covered in an old cloth and thrown back in the face of the person who performed it. The Salah then states, ‘May Allah Ta’ala destroy you just as you destroyed me.’ (Kanz al 'Ummal, Tabarani)
Summarizing the points in the above texts, Imam Ibn al-Qayyim R.A. writes,
"Six matters that are linked to the prayer have been indicated as marks of hypocrisy:
1) Laziness when one stands up to pray.
2) Intending to show off with one's prayer.
3) Delaying the prayer.
4) Praying in an extremely hasty manner.
5) Barely remembering Allah during the prayer.
6) Abandoning the congregational prayer."
-[Hukm Tarik al-Salat, p. 105]
How many of these are we guilty of?!
And, if this is the case with those who actually PRAY and demonstrate these signs, how about those who do not even pray in the first place?!
O Allah! Make us and our progeny from those who establish the prayer!