In Matthew 19:6 (= Mark 10:9) Jesus quotes Genesis 2:24, and then says, “what God has joined together, let man not separate”.

R. Paul Stevens discusses three approaches to the vexed question of remarriage after divorce: (a) the textual/legal approach, which seeks to find out what Scripture says about permissible grounds; (b) a dispensational approach which asks whether the harder teaching of the Bible is for our own day or some other age; and (c) through a biblical theology approach, which seeks to connect the reality of Scripture with the reality of contemporary culture.

In pursuing the third of these lines of enquiry, Stevens asks if there are marriages in which God has not joined the two together; where the union is neither blessed by God nor founded in God?  Karl Barth’s teaching on this subject is summarised:-

1. Marriage is an indissoluble union.  Whoever enters marriage must do so without any thought of leaving it.  The door marked ‘exit’ must be locked, and the key thrown away.
2. Even a well-married couple should not presume on God’s grace, or think that they can maintain a strong relationship without his help.
3. It is not possible to tell if one’s marriage is one not blessed by God, for God’s blessing may be hidden for the time being.  Therefore, a couple whose marriage is in trouble should consider that their relationship may be healed and their union given permanence.
4. Married couples should not rely on external indications of ‘success’, but rather on the call and provision of God; to the ‘yes’ of his promise, rather than to the ‘no’ of his judgement.
5. However, in an extreme case, we may painfully conclude that a given marriage is a noncovenant, and that the couple should not remain married.
6. The church must show compassion towards those who are divorced.  Indeed, those who have been blessed with ‘good’ marriages are in a supreme position to express something of the divine mercy towards those who have not been thus blessed.
7. Divorced persons must not be refused remarriage.  It is true that they have experienced God’s judgement in their (non-covenant) marriages.  But if they turn in repentance to Christ they may know the new beginning – either in marriage or in single life – that the gospel brings.
8. The big question is not divorce but marriage.  The human institution of marriage is dissoluble, but God’s covenant of marriage is indissoluble.

(Complete Handbook of Everyday Christianity, art. ‘Divorce’)