Why did Allah not protect the first book He sent down, but rather waited for the fifth book before promising to protect it?

God (Allah)Divine Wisdom
Why did Allah not protect the first book He sent down, but rather waited for the fifth book before promising to protect it?
Amina Inloes, Amina Inloes is originally from the US and has a PhD in Islamic Studies from the University of Exeter on Shi'a hadith. She is the program leader for the MA Islamic Studies program at the... Answered 6 years ago

Perhaps Allah willed to test human beings, since a repeated principle in the Quran and hadith is that Allah gives people repeated chances to prove themselves and make the best decisions before intervening in a situation. 

Maybe there is some other wisdom behind this also.