By Shaikh Muhammad bin Jameel Zainoo is one of the contemporary scholars of Islam. A student of Shaikh Al-Albaanee, he has written many valuable works on Islam. Source: The Methodology of the Saved Sect.
The Excellence of Tawhid
1) Allaah the Most High says: Those who believe and do not mix their belief with dhulm, they are those upon whom is security and they are the rightly guided. [6:82]
From 'Abdullaah ibn Mas'ood, who said: When this verse was revealed, some Muslims began to grieve, and said: 'Which of us does not do dhulm (oppression) to his soul?' The Messenger of Allaah said: "It is not that, verily it is shirk, have you not heard the saying of Luqmaan to his son: Oh my Son! Do not make shirk with Allaah. Verily, shirk is a great dhulm.[31:13] [Bukhari & Muslim]
This verse gives glad tidings to the believers, those who single out Allaah alone for worship, those who do not mix their belief with shirk. Rather, they are far from it, they have complete security from the punishment of Allaah in the Hereafter and they are the rightly guided in this world.
2) The Prophet said: "Imaan consists of sixty something branches, the highest of them is the saying 'Laa ilaaha illa Allaah; and the lowest of them is to remove something harmful from the road." [Muslim]
3) Shaikh 'Abdullaah Khayaat mentions in his book entitled Daleel ul-Muslim Fil I'tiqaad wat-Tat-heer. "Because of the human nature of man and due to his lack of infallibility, his feet slip and he falls into disobedience to Allaah. When he is from the people of tawheed, pure from the blemishes of shirk, and he singles out Allaah alone for worship, and he is sincere in saying 'Laa ilaaha illa Allaah' it becomes the greatest factor for his happiness and an expiation for his sins and an elimination of his evil deeds, as has come in the hadeeth of the Messenger of Allaah: " Whoever testifies that none has the right to he worshipped except A llaah, alone without any partners and that Muhammad is His slave and His messenger and that 'Eesaa is a slave of Allaah, and a Word delivered to Maryam and a Spirit from Him, and that Paradise is true and the Fire is true, Allaah will enter him into Paradise in accordance to his deeds." [Bukhari & Muslim]
Verily, 'Laa ilaaha illa Allaah', the testification that the Muslim testifies with, is the foundation necessary for his entrance into Paradise, the place of comfort, even if some of his actions had defects and shortcomings. As has come in the hadeeth Qudsee, Allaah, the Most High, says: "O Son of Aadam, verily If you were to come to Me with the equivalent of the earth full of mistakes and then meet Me without associating partners with Me in anything then I would give to you its equivalent amount of Mercy. [Hasan - Tirmidhi & ad-Diyaa]
Meaning: If one of you came to Me with an equivalent amount of the earth full of sins and disobedience, but you died upon tawheed, then I would forgive your sins.
It is reported from the Prophet that he said: "Whoever meets Allaah without having associated with Him in anything will enter Paradise and whosoever meets Him associating partners with him in anything will enter the Fire. " [Muslim]
All these narrations clearly show the Excellence of Tawheed, for it is that by which the happiness of the slave is achieved and the best means for the expiation of his sins and the elimination of his mistakes."