"Therefore let all the house of Israel know for certain that God has made Him both Lord and Christ-- this Jesus whom you crucified." (Acts 2:36)
What do you know for sure? Not just what do you think you know or believe to be sure, but what do you really know for sure? This is not a trick question. What you know for sure and believe about the Lord Jesus Christ will determine where you will spend eternity, either in heaven or hell.
For most people, when it comes to the important matters of life and death and the gospel of the Lord Jesus Christ, they don't know what they don't know. They are truly "spiritually" blind; But a natural man does not accept the things of the Spirit of God, for they are foolishness to him; and he cannot understand them, because they are spiritually appraised. (1 Corinthians 2:14)
The government, the ones who have the responsibility and authority to make and enforce the speed limits, warns drivers with traffic signs. God also warns us all by revealing His righteousness in what he has created; For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. (Romans 1:20)
There is enough "general" revelation in creation about God and His required righteousness and godliness to convict everyone of sin and pass judgment on every guilty soul, so that they are without excuse. And then the word of God gives us "specific" revelation regarding God, His righteousness and coming judgment, our sin and the saving gospel of the Lord Jesus Christ.
By the way, ignorance of the law is never a legitimate defense. If I'm caught speeding (which has unfortunately happened), pleading ignorance of the speed limit (which I have tried), won't stop the police officer from giving me a speeding ticket (which I have received and had to pay). The same is true of God's laws. The penalty for sin, even sinning in ignorance, is death--eternal separation for God in hell; For the wages of sin is death...(Romans 6:23)
Even if we may not know much for sure, this one thing we can know for sure; For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life. (John 3:16)