What does "Til death us do part" mean?

In a common wedding ceremony, the words “until death us do part” is often said as a final sentence. What does this mean?

Therefore what God has joined together, no human being must separate.

- Mark 10:9

Baltimore Catechism:

Q. 1023. Can the bond of Christian marriage be dissolved by any human power?
A. The bond of Christian marriage cannot be dissolved by any human power.

Q. 1025. Does not the Church sometimes allow husband and wife to separate and live apart?
A. The Church sometimes, for very good reasons, does allow husband and wife to separate and live apart; but that is not dissolving the bond of marriage, or divorce as it is called, for though separated they are still husband and wife, and neither can marry again till the other dies.

Marriage is a life long commitment. Each spouse is committed to the other until the death of one of them. Even if they separate/divorce they cannot remarry until the other spouse passes away (1 Cor 7:10-11). A widow or widower, however, is free to remarry (1 Cor 7:8-9).

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