A carpenter to a carpenter

Your trade was mine; your craft, I lay no claim to.
  I make my dealings square, which may suffice
  To brace as Augustine bid: Plain, free from vice,
I keep my spirit level, or I aim to;
To hold at length my temple from my bank,
  I render unto Caesar what is Caesar’s,
  The splinter in my eye excise with tweezers,
And do the same, or try to, with the plank.
One job alone has robbed me of my slumber,
  Ordained by one I can’t refuse a task,
A simple job: Just two plain posts of lumber,
No inlay—No fine lacquerwork—No gilt.
  I’ve never asked much of you; now I ask,
By whose hands—God or man—the Cross was built?