(This is an excerpt from a chapter by C.J. Mahaney, entitled: The Pastor's Priorities: Watch Your Life and Doctrine in the book: Preaching the Cross, by Mark Dever, J. Ligon Duncan III, R. Albert Mohler Jr. and C.J. Mahaney. Crossway Books, 2007. For more information about the ministry of these men, go to t4g.org)

[...] As we watch our doctrine, we must never forget that which is
central to our doctrine; the Gospel of Jesus Christ. If you fail to keep
the gospel at the core of your life and ministry, you have ceased to
watch your doctrine closely. "The preachers' commission," writes J.I.
Packer, "is to declare the whole counsel of God; but the cross is the
center of that counsel, and the Puritans knew that the traveler through
the Bible landscape misses his way as soon as he loses sight of the hill
called Calvery."

In all our preaching, we must never lose sight of the hill called
Calvery, where the Son of Man was killed in our place. Regardless of the
text or topic at hand, there must be some view of Calvery in every
sermon. Your congregation should experience the amazing and comforting
sight of the crucified Saviour each and every time you preach. They
should anticipate the sight of Calvery in every sermon and rejoice when
it comes into view, and all the more when the cross is not emmediately
obvious in the text. "Where is the hill?" they should be asking. "Where
is that blessed hill on which our precious saviour died?" We should
exalt Christ's finished work in our sermons so as to comfort the
converted and convict the unbeliever.

Spurgeon's example should inspire us: "I received some years ago orders
from my Master to stand at the foot of the cross until he comes. He has
not come yet, but I mean to stand there until he does." Let us stand
with the prince of preachers, gentlemen. As we preach the whole counsel
of God, let us keep the cross central. By doing so, we will indeed be
watching our doctrine.