Belief in Allah and Tauheed (One ness of Allah)
Allah says in the Qur'an:
 "He is the Lord of the heavens and the Earth and all that is in between them, so worship Him and be patient in His worship; do you know any equal to Him?" (19:65).
Tauheed is anchor sheet for a muslim
Obviously the most important of a muslim life is Tauheed (the oneness of Allah), this is like base and anchor sheet of Iman as all beliefs and actions are the command of Allah so tauheed and Iman of a muslim should be very firm and strong. He should have strong YAQEEN in his heart that only Allah has power to do the things.
"Allah there is no God but He, the Living, the Everlasting. Slumber does not seize Him, neither sleep; to Him belongs all that is in the heavens and the Earth. Who is there that shall intercede with Him except by His permission? He knows what is before them and what is behind them, and they do not encompass anything of His knowledge except what He wills. His throne extends over the heavens and the Earth, the preservation of them does not burden Him; He is the High, the Great" (2:255).
He has no associate in His divinity, His God ship, His names, or His attributes.
(Some scholars name these three as tauheed Uluhiat,Rububiat and Asma us Sifat respectively. Some other classify only in Raboobiat and Asma us sifat.And there is no controversy about its naming even if these classification is not mentioned in any hadith but has been done by scholars for better understanding)
Allah says
 "He is Allah, there is no god but He, the Knower of the Unseen and the Visible. He is the Most Gracious, Most Merciful. He is Allah, there is no God but He, the King, the Holy One, the Source of Peace, the Keeper of Faith, the Guardian, the Almighty, the Subduer, the Sublime. Glory be to Allah above what they associate with Him. He is Allah, the Creator, the Maker, the Shaper. His are the most beautiful Names. All that is in the heavens and the Earth glorifies Him. He is the Almighty, the Wise" (59:22-4).

Allah is the only master of benefit & loss
 Only Allah is the master of all happening benefit /loss. If he wills to give benefit/ make successful all the powers and superpowers cannot prevent it. If decides to keep in loss/make unsuccessful no superpower can save. He should have yaqeen that any person, any relation,any position,any degree,any amount of wealth,  cannot help unless Allah wills for that. Success is not in Kingship as Firaun failed in kingship, not in wealth as Qarun failed in wealth.
Allah can bring disgrace even in the presence of kingdom and wealth, and he can bring honour even in the state of dire poverty.
A human's internal treasure is his yaqeen (Faith), and his a’mal (action); if his inner actions are good then Allah will create a state of inner success, even if material possession is totally exhausted.
Whatever is made by Allah is under Allah’s. He owns everything. He uses everything and Allah can change shapes of everything by his power and he can change their qualities without changing their shapes. He can change a stick into a snake and a snake into a stick. Similarly he controls everything whether land (kingdom) or wealth, electrical or gaseous. He uses these things as he likes. He can bring about destruction from the means of creations and he can show creation from the means of destruction.He runs the system of sustenance. If he wishes he can sustain somebody in a barren desert without any source of material and he can spoil life even in the midst of plenty of materials.

 "He creates what He pleases. He gives, to whom He wills, females, and He gives, to whom He wills, males, or He couples them, males and females; and He makes whom He wills barren. Surely, He is the Knowing, the Powerful" (42:49-50).
"there is nothing whatever like unto Him, He is the All-hearing, the All-seeing. To Him belongs the keys of the Heavens and the Earth. He enlarges and restricts provisions to whom He wills. Surely He has knowledge of everything" (42:11-12).
 "there is no creature that moves on the Earth but its provision depends on Allah. He knows its dwelling and its resting place. All is recorded in a clear book" (11:6).
We believe that "with Him are the keys of the unseen; none knows them but He. He knows what is in land and sea; not a leaf falls, but He knows it. Not a grain in the deep darkness of the Earth, not a thing green or dry but it is in a clear Book" (6 :5 9 ).
We believe that "Allah alone has the knowledge of the Hour, sends down rain, and knows what is in the wombs. No soul knows what it shall earn tomorrow, and no soul knows in what land it shall die. Surely, Allah is All-knowing, All-aware" (31:34).
We believe that "if the ocean became ink for the words of my Lord, the ocean would be finished before the words of my Lord came to an end" (18:109); "And if all the trees that are in the earth were pens, and the ocean (were ink), with seven oceans swelling it therefore, the words of Allah would not be exhausted. Surely, Allah is Mighty, Wise" (31 :27).
We believe that Allah's words are the most truthful in conveying information, the most just in ruling, and the fairest in conversation. He said: "The word of your Lord has been fulfilled in truth and justice" (6:115); "And who is more truthful in his word than Allah?" (4:87).
We believe that the Qur'an is Allah's word. He literally spoke it to Gabriel, who conveyed it to the Prophet, peace be upon him: "Say (O Muhammad) 'the Holy Spirit has brought it down from your Lord in truth"' (16:102); "Truly it is the revelation of the Lord of the world brought down upon your heart by the Faithful Spirit so that you may be one of the warners, in a clear Arabic tongue" (26:192-95).
We believe that Allah is well above His creatures in His Person and His Attributes, because He says: "He is the High, the Great" (2:22); "He is Supreme over His servants, and He is the Wise, the All-aware" (6:18 ).
We Believe in Allah's Lordship, Oneness, and Attributes:
We believe in Allah's god ship; that is, He is the true God and every other so-called deity is false.No one should be worshiped other than him.
We believe in His names and attributes, that is He has the most magnificent names and the sublime perfect attributes.No one is sharing

We believe in Allah's divinity; that is he is the Lord, the Creator, the Sovereign, and the Manager of all affairs. He is the Rab the sole incharge of success and failure. He is the decision maker for all happiness and sorrow. He can make successful even if all human and power don’t want so. And he can make unsuccessful even all powers want to make successful. He can bring success in the arrangement and likeky unsuccessful situation and can bring failure in the likely successful situation. No power,or superpower ,no position or wealth, planning can bring a single piece of success without his consent.All other are helpless
Allah can bring disgrace even in the presence of kingdom and wealth, and he can
bring honour even in the state of dire poverty. A human's internal treasure is his yaqeen (Faith), and his a’mal (action); if his inner actions are good then Allah will create a state of inner success, even if material possession is totally exhausted.

La ilaha illallah demands a change of our faith and zazba, (thoughts, temperament),and our ways. Just by changing the yaqeen (faith) Allah has promised a paradise many times the size of this universe. Allah will subdue (bring under our control) all those materials from which we have changed our faith.

Dawah is to bring Yaqeen on Tauheed

To acquire this yaqeen in our life.We have to invite (dawaah) others for this yaqeen. Explain the greatness of Allah and explain the kudrat (power) of Allah. To describe his rububiyat (the
total sustenance and maintenance power) we will have to relate incidents from the lives of the prophets and companions.
2. We will have to think about it in solitude and get this same yaqeen to enter in
our heart, to which we gave dawaah in gatherings. That is the truth.
3. And then we have to cry to Allah, beg him to grant us the reality of this yaqeen.

It is  an integral part of a Muslim life, so he starts his  life with Tawheed and  ends his life with Tawheed. So we should pray Allaah to make the statement of Laa ilaaha lila Allaah) our last words in this world. And we should firm our faith in heart that only Allah is the  Still it is not enough ,a muslim duty is also to call mankind towards tauheed and strong Yaqeen  as The Holy Prophet Muhammad (Peace be on him) is the last prophet and no prophet will come till the day of judgment.And the ummah of Hazrat Muhammad (Sallallahu Alaihi Wasallam) has been assigned the duty to reach with this massage to whole mankind.