What has exceedingly hurt you in time past, nay, and I fear, to this day, is want of reading. I scarce ever knew a preacher who read so little. And perhaps, by neglecting it, you have lost the taste for it. Hence your talent in preaching does not increase. It is just the same as it was seven years ago. It is lively, but not deep; there is little variety; there is no compass of thought. Reading only can supply this, with meditation and daily prayer. You wrong yourself greatly by omitting this. You can never be a deep preacher without it, any more than a thorough Christian. Oh begin! Fix some part of every day for private exercises. You may acquire the taste which you have not; what is tedious at first will afterwards be pleasant. Whether you like it or no, read and pray daily. It is for your life; there is no other way; else you will be a trifler all your days, and a pretty, superficial preacher. Do justice to your own soul; give it time and means to grow. Do not starve yourself any longer. Take up your cross and be a Christian altogether. Then will all the children of God rejoice (not grieve) over you; and in particular yours.
– Quoted in D. A. Carson and John D. Woodbridge, Letters Along The Way, page 169.
(HT: Ray Ortlund)