can not understand GOD

until now i still can not understand GOD forever
why GOD let devil live do many bad things ?
why GOD let devil use disease kill father ?
why GOD let me live in many problems ?
why GOD created me live in weakness ?
why GOD created good and bad things ?
why GOD created all must live in destiny ?
why GOD created everything have problems ?
why why why why why why why why why why ?