Ecclesiastes (Temporal vs. Eternal)
Ignorance isn't an excuse
As Solomon concludes, when you are walking this life, we cannot put ignorance as an excuse to live the way we did. Contrary to God, all must answer to God and remember what Christ did on the cross.
Solomon's final book is full of lessons on living for what is eternal. After a life full of sin, Solomon looks back with regret and writes about his prodigal time running from God.