So, great physicians cannot all attend,
But some they visit, and to some they send.
Yet all those letters were not writ to all;
Nor first intended but occasional,
Their absent sermons; nor, if they contain
All needful doctrines, are those doctrines plain.
Clearness by frequent preaching must be wrought
They writ but seldom, but they daily taught;
And what one saint has said of holy Paul,
"He darkly writ," is true applied to all.