Basmallah is the word that is denoted to refer to the whole phrase of Bismillahir Rahmanir Raheem. It is said to contain all the three forms of Tawheed. To make it clear, Allah can be considered one and unique from three aspects.
When you say Bismillahir-Rahmaanir-Raheem, you are exerting your entire Tawheed to Allah in that matter that you are saying Bismillah to. It has all aspects of Tawheed in it. When you say Bismillah, you are saying Bismillah, Allah permits me to do this, Athinallahu Lee (أذن الله لي ). And if Allah did not permit me, I would not do it. So when you are saying Bismillah, you are saying I am doing it for the sake of Allah because Allah permitted me to do this. Allah allowed me to do this, Athinallahu Lee. I am doing it for Your sake Yaa Allah because You permitted and allowed me to do this.
That is why you do not say Bismillah when you are committing a sin, may Allah guard us and protect us from that. If someone is drinking alcohol, Laa Samahallah (لا سمح الله ), they do not say Bismillah. You do not say Bismillah because if you say Bismillah, you are actually getting two sins. You are saying that Allah permitted you and Allah never permitted that, and you are getting the actual sin for drinking the alcohol. So you are getting two sins if you do say Bismillah, even though believe it or not it is a trend in some Muslim countries that they say Bismillah before drinking alcohol.
That is Tawheed al-Uloohiyyah (توحيد الألوهية ). Bismillah, Allah permitted me to do this, I am doing this for the sake of Allah. We are doing this by the permission of Allah, this is Tawheed al-Uloohiyyah.
When you write down, who gave you the power to write? Allah gave you the power to write. So when you say Bismillah, you are saying I could not have done this without the power Allah has given me. Bismillah, I do this by the power Allah has given me. Bismillah I eat, because Allah has given me this provision and because had it not been for the power Allah has given me, I would not be able to chew it. Bismillah I write, because if it was not for Allah giving me the power, my hand would not be able to move (it would be paralysed). That is like saying Laa Hawla wa Laa Quwwata Illah Billah ( لا حول ولا قوة إلا بالله ). If it was not for the power that Allah has given me to do this act, I would not have done this act.
That is why Allah says:
﴾ و ما بِكُم مِّن نِّ عْ مةٍ ف مِ ن اللَّ هِ … ﴿النحل: ٣٥
And whatever of blessings and good things you have, it is from Allah. (Surat an-Nahl: 53)
Every provision you have is from Allah. So that is the second aspect, that is Tawheed ar-Rububiyyah (توحيد الربوبية ).
TAWHEED AL-ASMAA’ WAS-SIFAAT
You are seeking blessing by the name of Allah. Bismillah, you are using the name of Allah to bless whatever you are doing. When you are using the name of Allah and then following with Ar-Rahmaan and Ar-Raheem, those are names, qualities and attributes of Allah that we will discuss Inshaa Allah. You are using the name of Allah to bless the act you are doing, so that is Tawheed al-Asmaa’ was-Sifaat (توحيد الأسماء والصفات ). That applies to any matter that you say Bismillahir-Rahmaanir-Raheem (Basmalah) to.
When I say Bismillah to eat or to sit an exam for example, I say Bismillah to bless that matter (that is Asmaa’ was-Sifaat). Allah gave me the power to eat or to write, that is Rububiyyah. I do this for the sake of Allah, by the permission of Allah, He permitted me to do this and it is Halaal so I am doing it, that is Tawheed al-Uloohiyyah. And likewise, take it for everything else. When you say Bismillah, now you are going to get a different perspective of why you are saying Bismillah. Sometimes you are saying it because you read a Hadith to say it, now you understand why you are saying it.