It would be very wrong to judge divorced persons or to say that they are not welcome in the church - or to make them feel unwelcome in any way. It is a remarriage outside the church after a civil divorce that does separate one from the church's sacramental life. If the divorced are remarried civilly, they find themselves in a situation that objectively contravenes God's law. Consequently, they cannot receive Eucharistic communion as long as this situation persists. For the same reason, they cannot exercise certain ecclesial responsibilities.
People commonly think that divorce ends a marriage.
While that may be true from a civil law point of view, it is not the church's view. Once there is a marriage, it doesn't end, except by death. Society says, 'If you're divorced, the marriage is over. Well, we think that the marriage is not over. A valid, sacramental marriage is permanent.