Violence...The Verses

Verse (25:52)

The Verse says:
"So, (O Prophet), do not follow the unbelievers but engage in a mighty striving against them with this Qur'an." (25:52)

I cannot really imagine why this verse is considered a verse of violence, me personally I think it is exactly the opposite. God is ordering the noble prophet, peace and blessings be upon him, not to follow the unbelievers and ordering him to fight them by The Holy Quran (which is a book not a sword as you surely know) which means that you fight them by reason and convincing using the book revealed on you not the sword. Islam invaded hearts by its strong reason and logical arguments, meaning that reasoning the main" weapon" and to help us achieve this we are armed with "Holy Quran" where there are lots of logical discussions to be used when arguing with an unbeliever.

That's why the verse right after that one says:" And He it is Who has joined the two seas: one sweet and palatable and the other saltish and bitter; and He has set a barrier and an insurmountable obstruction between the two that keeps them apart. (25:53) And He it is Who has created man from water and then produced from him two sorts of kindred: by descent and by marriage. Your Lord is All-Powerful. (25:54) " you see now, the verses right after are all verses explaining God's blessings for mankind (so the unbelievers can reconsider their situation) so He explains the phenomena that sweet and salty water never mix. In the later verse He explains the miracle of the birth of man from a mere sperm drop .

A God arguing with His creation to make them believe in Him, how modest and kind of God to even consider convincing us with the obvious and even order His noble prophet, peace and blessings be upon him, to argue with the unbelievers and try to logically convince them with His existence and worthiness of love and worship and his only weapon here is "a book" namely the Holy Quran. How is that violence I can't possibly understand.