When one says “Bismillaah” when starting to do anything, what that means is, “I start this action accompanied by the name of Allaah or seeking help through the name of Allaah, seeking blessing thereby. Allaah is God, the beloved and worshipped, to Whom hearts turn in love, veneration and obedience (worship). He is al-Rahmaan (the Most Gracious) Whose attribute is vast mercy; and al-Raheem (the Most Merciful) Who causes that mercy to reach His creation.
It was said that what this means is: I start this action by mentioning the name of Allaah. Ibn Jareer (may Allaah have mercy on him) said: “Allaaah, may He be exalted and His name sanctified, taught His Prophet Muhammad (peace and blessings of Allaah be upon him) proper manners by teaching him to mention His most beautiful names before all his actions. He commanded him to mention these attributes before starting to do anything, and made what He taught him a way for all people to follow before starting anything, words to be written at the beginning of their letters and books. The apparent meaning of these words indicates exactly what is meant by them, and it does not need to be spelled out.”
There is something omitted in the phrase “Bismillaah” when it said before starting to do something, which may be “I begin my action in the name of Allaah,” such as saying, “In the name of Allaah I read”, “In the name of Allaah I write”, “In the name of Allaah I ride”, and so on. Or, “My starting is in the name of Allaah”, “My riding is in the name of Allaah”, “My reading is in the name of Allaah”, and so on. It may be that blessing comes by saying the name of Allaah first, and that also conveys the meaning of starting only in the name of Allaah and not in the name of anyone else.
The name of Allaah is the greatest name and is so well known as to need no explanation; this is a name that belongs exclusively to the Creator and no one else. The correct view is that it is derived from the root aliha. He is God (ilaah) which means that He is worshipped and is divine.
Al-Rahmaan is one of the names of Allaah that belong exclusively to Him. It means the One Who possesses vast mercy, because this form (fa’laan) is indicative of fullness and abundance. It is the most exclusive name of Allaah after His name Allaah, just as mercy is His most exclusive attribute. Hence this name (al-Rahmaan) often appears after the name Allaah, as in the aayah (interpretation of the meaning):
“Say (O Muhammad): Invoke Allaah or invoke the Most Gracious [al-Rahmaan] (Allaah)” [al-Isra’ 17:110]
Al-Raheem is also one of the names of Allaah, and means the One Who causes His mercy to reach those whom He wills among His slaves.
Ibn al-Qayyim (may Allaah have mercy on him) said: “Al-Rahmaan refers to an attribute that is connected to Allaah and is part of His Essence, and al-Raheem refers to a connection with the one to whom mercy is shown. The former is adjectival (referring to what He is) and the latter is verbal (referring to what He does). The former indicates that mercy is His attribute, and the latter indicates that He bestows His mercy upon His creation. If you want to understand this then ponder the meaning of these verses (interpretation of the meanings):
“And He is Ever Most Merciful (Raheem) to the believers”[al-Ahzaab 33:43]
“Certainly, He is unto them full of kindness, Most Merciful (Raheem)” [al-Tawbah 9:117]
The word al-Rahmaan is never used in this context. So we know that the word Rahmaan means the One Whose attribute is mercy (rahmah), and al-Raheem is the One Who bestows His mercy.”
(Badaa’i’ al-Fawaa’id, 1/24).