The True Church according to The Belgic Confession

We believe and confess
one single catholic or universal church--
a holy congregation and gathering
of true Christian believers,
awaiting their entire salvation in Jesus Christ
being washed by his blood,
and sanctified and sealed by the Holy Spirit.

As for those who can belong to the church,
we can recognize them by the distinguishing marks of Christians:
namely by faith,
and by their fleeing from sin and pursuing righteousness,
once they have received the one and only Savior,
Jesus Christ.
They love the true God and their neighbors,
without turning to the right or left,
and they crucify the flesh and its works.

Though great weakness remains in them,
they fight against it
by the Spirit
all the days of their lives,
appealing constantly
to the blood, suffering, death, and obedience of the Lord Jesus,
in whom they have forgiveness of their sins,
through faith in him.

--from the Belgic Confession, articles 27 & 29