What is the Day of Atonement?

What does the Day of Atonement mean for mankind? After the return of Christ this will be the first time people will have their minds open to the truth.

I was baptized in 1976. Married to Kathy Gaugler in 1977. We have 5 children and 12 grandchildren. We have our own general contracting business. We live on a little farmette in rural Pennsylvania.