It is a shame to lose such a family heirloom. Sometimes these things are sold when one falls into hard times or are just lost, or even stolen.
This Christian would be Johan Kristian Johnsen Ertzgaard (Ertsgård) born 11 Feb 1888 on Nestrøen, Ertsgård farm, Stjørdal, Nord-Trøndelag, Norway which is near Trondheim. They emigrated in 1888 so 'Christian' would only have been a baby when he arrived in the USA.
Even though you are not related to the Ertzgaards, I am sure you will treasure this portrait as if it was one of your own family and therefore it will live throughout eternity.