Why was a restoration necessary?

During His mortal ministry, Jesus Christ established His Church with priesthood authority. It was led by prophets and apostles who taught true doctrine and received revelation that was recorded as scripture. With the death of the apostles, priesthood authority was taken from the earth, revelation ceased, and essential doctrines were lost or corrupted. Through the Prophet Joseph Smith, the Church that Jesus Christ established was restored.

https://www.lds.org/youth/learn/yw/apostasy-restoration/restoration?lang=eng

why was a restoration necessary 2.jpg1.84 MB

why was a restoration necessary.jpg2.95 MB