Looks to be the "serenity prayer" which is associated with many 12 step programs.
God, grant me the serenity
To accept the things I cannot change,
The courage to change the things I can,
And the wisdom to know the difference.
Did a little google research and the original version is a little longer and was first attributed to Reinhold Niebuhr in 1939. However he claimed he did not originally pen this and actually credits Friedrich Oetinger (1702 - 1782), an 18th century theologian, for writing it.
Oetinger's version is:
"God give me the detachment to accept those things I cannot alter;
the courage to alter those things I can alter;
and the wisdom to distinguish the one thing from the other."
But, Oetinger's version is reportedly based on "The first form of the prayer,", originated with Boethius, the Roman philosopher (480-524 A.D.), and author of the book, Consolations of Philosophy.
Errr.... Ok, none of this drivil helps to date your piece, but that's what I suspect it is. A icon of the prayer. I suspect since it uses the key words from the modern version it is a fairly modern piece (post 1939 at least).