Praise be to Allah.
The importance of the prayer in Islam cannot be understated. It is the first pillar of Islam that the Prophet (peace and blessings be upon him) mentioned after mentioning the testimony of faith, by which one becomes a Muslim. It was made obligatory upon all the prophets and for all peoples. Allah has declared its obligatory status under majestic circumstances. For example, when Allah spoke directly to Moses, He said,
"And I have chosen you, so listen to that which is inspired to you. Verily, I am Allah! There is none worthy of worship but I, so worship Me and offer prayer perfectly for My remembrance." [Taha 13-14]
Similarly, the prayers were made obligatory upon the Prophet Muhammad (peace and blessings be upon him) during his ascension to heaven. Furthermore, when Allah praises the believers, such as in the beginning of Surah al-Muminun, one of the first descriptions He states is their adherence to the prayers.
Once a man asked the Prophet (peace and blessings be upon him) about the most virtuous deed. The Prophet (peace and blessings be upon him) stated that the most virtuous deed is the prayer. The man asked again and again. The first three times, the Prophet (peace and blessings be upon him) again answered, "The prayer," then on the fourth occasion he stated, "Jihad in the way of Allah." [This is from a hadith recorded by Ahmad and ibn Hibban. According to al-Albani, the hadith is hasan. Muhammad Nasir al-Din al-Albani, Sahih al-Targhib wa al-Tarhib (Beirut: al-Maktab al-Islami, 1982), vol. 1, p. 150]
The importance of prayer is demonstrated in many of the Prophet’s statements. For example, the Prophet (peace and blessings be upon him) said,
"The first matter that the slave will be brought to account for on the Day of Judgment is the prayer. If it is sound, then the rest of his deeds will be sound. And if it is bad, then the rest of his deeds will be bad." [Recorded by al-Tabarani. According to al-Albani, it is sahih. Al-Albani, (Sahih al-Jami’, vol.1, p. 503)
The importance of the prayers lies in the fact that no matter what actions one performs in his life, the most important aspect is one’s relationship to Allah, that is, one’s faith (iman), God-consciousness (taqwa), sincerity (ikhlas) and worship of Allah (`ibadah). This relationship with Allah is both demonstrated and put into practice, as well as improved and increased, by the prayer. Therefore, if the prayers are sound and proper, the rest of the deeds will be sound and proper; and if the prayers are not sound and proper, then the rest of the deeds will not be sound and proper, as the Prophet (peace be upon him) himself stated.
In reality, if the prayer is performed properly – with true remembrance of Allah and turning to Him for forgiveness – it will have a lasting effect on the person. After he finishes the prayer, his heart will be filled with the remembrance of Allah. He will be fearful as well as hopeful of Allah. After that experience, he will not want to move from that lofty position to one wherein he disobeys Allah. Allah has mentioned this aspect of the prayer when He has said,
"Verily, the prayer keeps one from the great sins and evil deeds" (al-Ankabut 45). An-Nadwi has described this effect in the following eloquent way,
Its aim is to generate within the subliminal self of man such spiritual power, light of faith and awareness of God as can enable him to strive successfully against all kinds of evils and temptations and remain steadfast at times of trial and adversity and protect himself against the weakness of the flesh and the mischief of immoderate appetites. [an_Nadwi, p. 24]
The overall effect that the properly performed prayers should have upon humans is described in other verses in the Quran:
"Verily, man was created impatient, irritable when evil touches him and withholding when good touches him. Except for those devoted to prayer those who remain constant in their prayers…" (al-Ma’arij 19-23).
As for the Hereafter, Allah’s forgiveness and pleasure is closely related to the prayers. The Messenger of Allah (peace and blessings be upon him) said,
"Allah has obligated five prayers . Whoever excellently performs their ablutions, prays them in their proper times, completes their bows, prostrations and khushu` [Khushu` in the prayer is where the person’s heart is attuned to the prayer. This feeling in the heart is then reflected on the body. The person remains still and calm. His gaze is also lowered. Even his voice is affected by this feeling in the heart. For more details on this concept (as well as the difference between it and khudhu`), see Muhammad al-Shayi’, al-Furuq al-Laughawiyyah wa Atharaha fi Tafsir al-Quran al-Karim (Riyadh: Maktabah al-Ubaikan, 1993), pp. 249-254.] has a promise from Allah that He will forgive him. And whoever does not do that has no promise from Allah. He may either forgive him or punish him." [Recorded by Malik, Ahmad, Abu Dawud, al-Nasai and others. According to al-Albani, it is sahih. Al-Albani, Sahih al-Jami’, vol. 1, p. 616.] ]
The prayers are a type of purification for a human being. He turns and meets with his Lord five times a day. As alluded to above, this repeated standing before Allah should keep the person from performing sins during the day. Furthermore, it should also be a time of remorse and repentance, such that he earnestly asks Allah for forgiveness for those sins that he committed. In addition, the prayer in itself is a good deed that wipes away some of the evil deeds that he performed. These points can be noted in the following hadith of the Prophet (peace be upon him):
"If a person had a stream outside his door and he bathed in it five times a day, do you think he would have any filth left on him?" The people said, "No filth would remain on him whatsoever." The Prophet (peace and blessings be upon him) then said, "That is like the five daily prayers: Allah wipes away the sins by them." (Recorded by al-Bukhari and Muslim.)
In another hadith, the Prophet (peace be upon him) said,
"The five daily prayers and the Friday Prayer until the Friday prayer are expiation for what is between them." (Recorded by Muslim)
And Allah knows best.