According to Protestants, what is the lesson being taught by scripture when God killed so many men for looking into the Ark? Many people find a short passage in the Old Testament to be both disturbing and very peculiar; that being 1st Samuel 6:19, 


  and He (God) smote (killed) the men of Beth-she-mesh, because they
  had looked into the Ark of the Lord, even He smote of the people
  50,070 men.  


The disturbing question is why God would kill so many men for simply looking into the Ark.  It seems to be a very peculiar thing to do.  One thing is obvious, God is using this event and recording it in His Word as a historical parable. A teaching lesson with a spiritual meaning.  

What is that meaning?

I am not attempting to ask God's motivation for killing these men; but I am asking, what God is teaching through this story?  Are there different interpretations of this lesson between the different denominations of Christianity?
Sin really did abound when the Law was given in the old testament, and every form of disobedience or sin, as little as it can be, was dealt with strict punishment or Death.

Jesus came to fulfil all laws (Matthew 5:17-20) and destroy sin and death. 
This means that we no longer live in sin but by Grace and we can walk boldly to his throne (Hebrews 4:16) without fear or guilt like Old Testament people. 

The Law has been abolished and Jesus took every judgement upon Himself.