Catholic ecclesiology is the theological study of the Catholic Church, its nature and organisation, as described in revelation or in philosophy. Such study shows a progressive development over time. Here the focus is on the time leading into and since the Second Vatican Council (1962-1965).

In Christian theology, the Christian Church is traditionally divided into:

the Church Militant (Latin: Ecclesia militans), which consists of Christians on earth who struggle as soldiers of Christ against sin, the devil, and “the rulers of the world of this darkness, against the spirits of wickedness in the high places”;
the Church Penitent (Latin: Ecclesia poenitens), also called the Church Suffering (Latin: Ecclesia dolens) or the Church Expectant (Latin: Ecclesia expectans), which in the theology of certain churches, especially that of the Catholic Church, consists of those Christians currently in Purgatory; and
the Church Triumphant (Latin: Ecclesia triumphans), which consists of those who have the beatific vision and are in Heaven.

These divisions are known as the three states of the Church, especially within Catholic ecclesiology. These divisions are often discussed in the context of the doctrine of the communion of saints; although Christians may be physically separated from each other by the barrier of death, they nonetheless remain united to each other in one Church, and support each other in prayer.

The Church Triumphant
The term triumphant (Latin: triumphans), means “exulting, rejoicing exceedingly”, taken from a figurative usage of triumphus, originally designating the Roman triumph. Those who constitute the Church Triumphant rejoice eternally in the glory of God, to whom they are united in the beatific vision.

The Church Suffering

The term penitent (Latin: poenitens or paenitens means “repenting, being sorry”. Those who constitute the Church Penitent are in Purgatory to satisfy whatever portion of the temporal punishment due for their sins was not satisfied before death. They are in a process of purging their imperfections before entering heaven. It is held that all members of the Church Penitent will eventually join the Church Triumphant.

The alternate term suffering (Latin: dolens, lit. ‘grieving’) emphasizes the nature of souls’ experience in Purgatory; they are suffering the temporal consequences of their sins to redemptive effect. The other alternative, expectant (Latin: expectans or exspectans), emphasizes that the souls of Purgatory are awaiting expectantly the beatific vision of heaven.

The Church Militant

The term militant (Latin: militans) has a primary meaning of “being a soldier, performing military service”, but it acquired a secondary meaning of “serving, performing service, laboring”, with its root milito coming to mean “soldier of Christ or God” in Medieval Latin usage. The members of the Church Militant, i.e. those Christians on earth, are engaged in spiritual warfare against sin in order that, when they die, they might enter heaven and join the Church Triumphant. Failing that directly, those who believe in the existence of Purgatory hope to die in a state of grace and join the Church Penitent, to purify themselves of their imperfections and, ultimately, join the Church Triumphant.

The Catholic Church commemorates the Church Triumphant and the Church Penitent in its liturgy on two consecutive days: All Saints’ Day on November 1 (the Church Triumphant) and All Souls’ Day on November 2 (the Church Penitent).

These terms are not used in the Catechism of the Catholic Church, an authoritative summary of the teaching of the Catholic Church published in 1994. However, the teaching these terms represent is precisely restated, quoting Lumen gentium:

The three states of the Church. “When the Lord comes in glory, and all his angels with him, death will be no more and all things will be subject to him. But at the present time some of his disciples are pilgrims on earth. Others have died and are being purified, while still others are in glory, contemplating ‘in full light, God himself triune and one, exactly as he is’.”

Lumen Gentium