From Spurgeon's book, "Gleanings Among the Sheaves"

What is it to have "Christ in you?"

The Romanist hangs the cross on his bosom.

The true Christian carries the cross in his heart;
and a cross inside the heart is one of the
sweetest cures for a cross on the back.

If you have a cross in your heart -- Christ crucified in you,
the hope of glory, the cross of this world's troubles will seem
to you light enough, and you will easily be able to sustain it.

Christ in the heart means Christ believed in, Christ loved,
Christ trusted, Christ espoused, Christ communed with,
Christ as our daily food, and ourselves as the temple
and palace wherein Jesus Christ daily walks.

Ah! there are many who are total strangers to the meaning of
this phrase. They do not know what it is to have Jesus Christ
'in them'. Though they know a little about Christ on Calvary,
they know nothing about Christ in the heart.

Now, remember, that Christ on Calvary will save no man,
unless Christ is in the heart.

The Son of Mary, born in the manger, will not save you,
unless He is born also in your heart and lives there
-- your joy, your strength, and your consolation.