You would not suspect him to be a Christian

(Archibald Alexander, "The Backslider" 1844)

"You have forsaken your first love." Revelation 2:4

Backsliding occurs when the Christian is gradually led
off from close walking with God, loses the lively sense of
divine things, becomes too much attached to the world
and too much occupied with secular concerns; until at
length the keeping of the heart is neglected, prayer
and the seeking of the Lord in private are omitted or
slightly performed, zeal for the advancement of religion
is quenched, and many things once rejected by a
sensitive conscience are now indulged and defended.

All this may take place and continue long before the
person is aware of his danger, or acknowledges that
there has been any serious departure from God. The
'forms of religion' may still be kept up, and 'open sin'
avoided. But more commonly backsliders fall into some
evil habits--they are evidently too much conformed to
the world, and often go too far in participating in the
pleasures and amusements of the world.

Too often there is an indulgence in known sin into which
they are gradually led, and on account of which they
experience frequent compunction, and make solemn
resolutions to avoid it in future. But when the hour of
temptation comes, they are overcome again and again,
and thus they live a miserable life, enslaved by some sin,
over which, though they sometimes struggle hard, they
cannot get the victory.

There is no more inconsistent thing than a backsliding
Christian. Look at one side of his character and he seems
to have sincere, penitential feelings, and his heart to be
right in its purposes and aims; but look at the other side,
and he seems to be "carnal, sold under sin". O wretched
man! how he writhes often in anguish, and groans for
deliverance--but he is like Samson shorn of his locks--
his strength is departed, and he is not able to rise and
go forth at liberty as in former times.

The sleeping backslider is one who, being surrounded
with earthly comforts and engaged in secular pursuits,
and mingling much with the decent and respectable
people of the world, by degrees loses the deep impression
of divine and eternal things. His spiritual senses become
obtuse, and he has no longer the views and feelings of
one awake to the reality of spiritual things. His case nearly
resembles that of a man gradually sinking into sleep. Still
he sees dimly and hears indistinctly--but he is fast losing
the impression of the objects of the spiritual world, and is
sinking under the impression of the things of time and sense.

There may be no remarkable change in the external conduct
of such a person, except that he has no longer any relish for
pious conversation, and rather is disposed to waive it. The
difference between such a one and the rest of the world
becomes less and less distinguishable. From anything you
see or hear--you would not suspect him to be a
Christian, until you see him taking his seat at church!