23 Nor must one imagine that the Body of the Church, just because it bears the name of Christ, is made up during the days of its earthly pilgrimage only of members conspicuous for their holiness, or that it consists only of those whom God has predestined to eternal happiness. It is owing to the Savior's infinite mercy that place is allowed in His Mystical Body here below for those whom, of old, He did not exclude from the banquet. For not every sin, however grave it may be, is such as of its own nature to sever a man from the Body of the Church, as does schism or heresy or apostasy. Men may lose charity and divine grace through sin, thus becoming incapable of supernatural merit, and yet not be deprived of all life if they hold fast to faith and Christian hope, and if, illumined from above, they are spurred on by the interior promptings of the Holy Spirit to salutary fear and are moved to prayer and penance for their sins.
Source: Mystici Corporis Christi (Vatican.va)