Interpretation of Kitab At-Tauhid - The Destination of the Seeker of Truth
Author: Shaikh Salih bin 'Abdul-'Aziz bin Muhammad bin Ibraheem Aali Shaikh.
Publisher: Darussalam (01-May-03)
Pages: 325 (Hardback)
Here is a sample chapter from the book
Chapter 1: The Virtue of At-Tauhid and what Sins it Expiates
Allah the Most High said,
'Those who believe and do not mix their belief with any Dhulm, for them there is security and they are guided ones.' (6:82) 
'Ubaadah bin As-Saamit (R) narrated that Allah's Messenger; said,
'Whoever testifies that there is none worthy of being worshipped but Allah, Who has no partner, and that Muhammad is His slave and Messenger, and that 'Elsa (Jesus) is the Slave of Allah, His Messenger, and His Word which He bestowed in Maryann (Mary) and a spirit (created) from Him, and that Paradise is true, and that the Fire is true, Allah will admit him into Paradise, whatever his deeds may be. 
They (Al-Bukhari and Muslim) both recorded this Hadith. They (Al-Bukhari and Muslim) also recorded the Hadith of 'Itbaan:
'Indeed Allah has forbidden for Hell the person who says: 'There is nothing worthy of being worshipped but Allah,' seeking thereby the Face of Allah.' 
Abu Sa'eed AI-Khudri narrated that Allah's Messenger said,
'Musa (Moses) said: 'O my Lord, teach me something by which I can remember You and supplicate to You.' Allah answered: 'Say, O Musa, La ilaha illallah (none has the right to be worshipped but Allah).' Musa said: 'O my Lord, all your slaves say this.' Allah said: 'O Musa, if the seven heavens and all of their inhabitants besides Me, and the seven earths were in a pan (of a scale), and La ilaha illallah was in (another) pan, La ilaha illallah would outweigh them.'
Ibn Hibbaan and AI-Haakim recorded this, and he (AIHaakim) graded it authentic (Saheeh).
At-Tirmithi recorded a Hadith that he graded good (Hasan), from Anas (who said): 'I heard Allah's Messenger' ; saying,
'Allah the Most High said, 'O son of Aadam! If you came to Me with sins filling the earth, then you met Me without associating anything with Me, I would come to you with its (the earth's) fill of forgiveness.'' 
Important issues of the Chapter
1) The abundance of AIlah's favor.
2) The numerous rewards of At-Tauhid with Allah.
3) Along with this it expiates sins.
4) Explanation of the verse which is in Surah AI An'am (6:82).
5) Notice the five points in the Hadith of 'Ubaadah.
6) That when you combine it (the Hadith of 'Ubaadah) with the Hadith of 'Itbaan and that which follows it, the meaning of the statement La ilaha illallah becomes clear to you, and the mistake of those who have been deceived also becomes clear to you.
7) Drawing attention to the condition which is in the Hadith of 'Itbaan.
8) The fact that the Prophets needed to be made aware of the virtue of La ilaha illallah.
9) Drawing attention to its (the statement La ilaha illallah) outweighing all of creation, along with the fact that many of those who say it lighten its weight in the scale.
10) The text which proves that the earths are seven just as the heavens (are seven).
11) That they have inhabitants.
12) Confirmation of the attributes, contrary to (the understanding of) the Ash'ariyyah.
13) That if you know the Hadith of Anas, then you know that strong the Prophet's statement in the Hadith of 'Itbaan,
'Indeed Allah has forbidden for Hell the person who says, 'none has the right to be worshipped but Allah,' seeking thereby the Face of Allah,'
that it is by abandoning Ash-Shirk, not simply saying it with the tongue.
14) Notice the combined mentioning of both Isa (Jesus) and Muhammad as two Slaves of Allah and His Messengers.
15) Knowing that Isa was particularily as being the Word of Allah.
16) Knowing that he ('Isa Alay hes salam) was a spirit from Him (Allah).
17) Knowing the virtue of belief in Paradise and the Fire.
18) Knowing his (the Prophet's) statement, '...whatever his deeds may be.'
19) Knowing the AI-Meezaan (scale) has two pans.
20) Knowing the usage of the term 'Face' (of Allah).