Assalaamu 'Alaykum,
After reading and contemplating, I came to realize two matters but failed with a third concerning which I need your help.
1- I learned that all occurrences and laws until now lead us to the existence of a wise Creator.
2- I learned that everything until now leads us to the truthfulness of Muhammad as a Messenger. 3- How can we believe that the sender is the Creator and that we must apply all that He sent down to us?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The answer to your question is based on the second conclusion that you reached, which is your belief in the truthfulness of Muhammad, sallallaahu ‘alayhi wa sallam. The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, informed you that he was sent by Allaah, the Creator of this universe that was not created by any but Him.

Allaah The Almighty Says, commanding Muhammad, sallallaahu ‘alayhi wa sallam, (what means): {Say, [O Muhammad], ‘O mankind, indeed I am the Messenger of Allaah to you all, [from Him] to whom belongs the dominion of the heavens and the earth. There is no deity except Him; He gives life and causes death.’ So believe in Allaah and His Messenger, the unlettered Prophet, who believes in Allaah and His words, and follow him that you may be guided.} [Quran 7:158]

Furthermore, this honest Messenger, sallallaahu ‘alayhi wa sallam, informed us that Allaah ordered us to obey him and believe him in what he conveyed from Him. At this point a question may occur to your mind, which is, how could the Messenger, sallallaahu ‘alayhi wa sallam, be sure that he was addressed and commanded by Allaah The Almighty, the Creator of this universe? The answer is that Allaah The Exalted gives the person whom He chooses to be His Messenger insight and signs which will make him believe with certitude that the sender is indeed  Allaah The Almighty. Here, Allaah The Almighty Says (what means) concerning His Prophet Moosa (Moses) :

Moreover, Allaah The Almighty Says concerning Muhammad, sallallaahu ‘alayhi was sallam, (what means): {Exalted is He who took His Servant by night from Al-Masjid Al-Haraam to Al-Masjid Al-Aqsa, whose surroundings We have blessed, to show him of Our signs. Indeed, He is the Hearing, the Seeing.} [Quran 17:1]

Allaah Knows best.