In the Name of Allaah, the Most Merciful, the Bestower of Mercy; may the peace and blessings of Allaah be upon our Messenger, Muhammad, his family, his Companions and all of those who follow him in righteousness until the Last Day.
As to what proceeds:
The Effects Of
LAA ILAHAH ILALLAAH
By the esteemed Scholar Shaykh Saalih ibn Fawzaan al-Fawzaan 
The kalimah (word) Laa ilahah ilallaah (that none has the right to be worshipped except Allaah), if it said with truthfulness and sincerity from the heart, and acted upon in that which it necessitates - outwardly and inwardly - then its effect will indeed be praiseworthy upon both the individual and the society.
From the most important of its effects are:
 Uniting the word of the Muslims:
This will result in strengthening the Muslims and assisting them in defeating their enemies - as long as they continue to follow and practice the same single religion, and as long as they adhere to the same single 'aqeedah (belief). Allaah - the Most High - says:
"And hold fast altogether to the rope of Allaah and do not be divided."
[soorah Aal-'Imraan 3:103].
"It is He Who has strengthened you with His help and with the Believers, and moreover, He has put love and affection between their hearts. If you were to spend all that is in the earth, then never could you have united their hearts, but Allaah has united them. Indeed He is the all-Mighty, the all-Wise."
[soorah al-Anfaal 8:62-63].
And differing in matters of 'aqeedah (beliefs) is the cause for splitting, disunity and hostility, as Allaah - the Most High - says:
"Indeed those who split-up their religion and become sects, you have no part with them in the least."
[soorah al-An'aam 6:159]
"But people have cut-off their affair of unity between them and have become sects, each party rejoicing in that which is with itself."
[soorah al-Mu'minoon 23:53]
So people cannot truly be united except upon the correct concept of eemaan (faith) and the correct 'aqeedah of Tawheed (singling Allaah out, alone, without partner, with all acts of worship), which are both direct implications of Laa ilahah ilallaah. One need only consider the condition of the Arabs before and after Islaam.
 Prevalence of safety and peace in a unified society,
which believes in and abides by Laa ilahah ilallaah. Since the individuals in such a society will take care in doing only that which Allaah has made halaal (lawful) and abandoning that which Allaah has made haraam (unlawful) - acting in accordance with what the 'aqeedah necessitates upon them. So this will prevent people from enmity, oppression and injustice, whilst directing them towards co-operation, love and deep brotherhood for the sake of Allaah, acting upon His - the Most High's - saying:
"Indeed the Believers are but brothers."
[soorah al-Hujuraat 49:10]
This is clearly reflected in the life of the Arabs before and after believing in Laa ilahah ilallaah. Before Islaam, they lived in hostility and insecurity, constantly fighting and killing each other. However, when they embraced Islaam this all changed, and the same people lived with each other in peace and an atmosphere of love and brotherhood prevailed, as Allaah - the Most High - says:
"Muhammad is the Messenger of Allaah, and those who are with him are strong and mighty against the unbelievers and merciful and kind amongst each other."
[soorah al-Fath 48:29].
"And remember the favour of Allaah upon you; for you were enemies and He joined your hearts in love, so that by His grace you became brothers."
[soorah Aal-'Imraan 3:103].
 Achievement of happiness,
attainment of the khilaafah (succession of power and authority) in the earth, maintaining purity of the religion and being steadfastness against the onslaught of false beliefs and foreign ideologies. Allaah says:
"Allaah has promised to those amongst you who truly have eemaan (true faith and belief) and act in obedience to Allaah and His Messenger, that He will grant them rulership upon the earth, just as He granted it to those before them, and that He will establish their Religion for them and grant them the authority to practice their Religion which He chose and ordered them with. And He will certainly change their situation to one of security, after their fear. Providing that they worship and obey Me, not associating anything else in worship with Me. Then, whoever rejects this favour by disobedience to their Lord - then they are the rebellious transgressors."
[soorah an-Noor 24:55].
So Allaah - the Most Perfect - has made achievement of these lofty goals conditional upon worshipping and obeying Him and not associating any partners with Him. And this is the true meaning of Laa ilahah ilallaah.
 From Laa ilahah ilallaah, Ma'nahaa, Makaanatuhaa wa Fadluhaa (pp.36-39), abridged.