Simple (?) Form Value Update Question

I am trying to update the value in one field (RUS Prop Class Document) of a form based upon what is selected in another field (RUS Prop Class Code). I plan on this being a hidden field so I was creating an after update expression in [RUS Prop Class Code]. My problem is that the value returned is the very nice and working query but not the value of the query. I'm missing something that I think is simple but cannot figure out with my limited resources and late hours.

Here is what I have for the after update expression in [RUS Prop Class Code]:

Private Sub RUS_Prop_Class_Code_AfterUpdate()
[RUS Document].Value = "Select [tbl_List of RUS Classifications].[RUS Prop Class Document] " & _
"FROM [tbl_List of RUS Classifications] " & _
"WHERE [tbl_List of RUS Classifications].[RUS Prop Class ID] =" & Me.[RUS Prop Class Code] & ";"
End Sub

Thanks ahead of time