Cowpat : to try and clarify -
Resolve in direction of flight you have Thrust acting forward, drag backward and Weight also acts against thrust with a component of Wsin(theta).
Hence by equilibrium in a steady climb the sum os all forces acting forward = sum of all forces acting rearward, thus:
T = D + Wsin(theta)
Rearranging gives
(T-D)/W = sin(theta)
Hope this clarifies a little.
Greaser