What Must I Do To Be Saved?

In Acts 16: 25-34, we read about Paul and Silas who were imprisoned in the city of Philippi, and how the jailer who was watching guard over them became so moved that he was compelled to ask them the most important question in life: "What must I do to become saved?" Their answer:
... Believe on the Lord Jesus Christ, and thou shalt be saved !


Why is this such an important question?


What am I supposed to be saved from?


Why will believing in the Lord Jesus Christ save me?


Why is this such an important question?