and now need to seal it. Why?

I used satin wall paint and have a two year old grandson. I thought sealing it would protect the finish as this table will get heavy use and abuse.

Lots of people think that paint isn't a protective finish by itself, but this isn't really true. You can put some clear coats on top of the paint, but if the paint is high quality paint and it's satin, you probably will not gain any durability by doing that.

What he^ said

Thank you all for the information. Not upset at all that another step is not required!