The idea that the church is the bride of Christ is common in popular thinking, especially in hymns and songs. This is based on the common metaphor drawn from the Hebrew Bible that Israel is God’s bride. Beginning in Hosea, the prophets use the metaphor of a marriage relationship frequently to describe God’s relationship to his people. This metaphor is almost entirely negative since Israel was an unfaithful bride. Jesus employs similar language as the Hebrew prophets, calling his himself a bridegroom and comparing both his current ministry and future return to a wedding banquet (Mt 22:1-12, 25:1-14).
As the idea that the Church has replaced Israel as God’s people became dominant, it was quite easy to extend the metaphor of a marriage to the church. Just as the idea was common in the Hebrew Bible, so too the image of the church as the bride of Christ became pervasive in medieval theology and art. For many, the idea of the church as the bride of Christ is the dominant metaphor in their theology. But the basis for this metaphorical transfer is a replacement theology (even if it is implicit); anyone who rejects replacement theology will also think about the usefulness of this metaphor for the church.
It remains a fact, however, that Paul describes the church as a virgin being prepared for marriage in Eph 5:21-33. Christ’s love for the church is described in 5:25-26, 29. Paul cites foundational text for marriage in the Hebrew Bible (Gen 2) and draws an analogy from it. The relationship of Christ and church similar to that of the married couple – they are “one flesh” in Gen 2. Therefore there is some intimate connection between Christ and the church which can be described in similar terms.
There is something of an eschatological perspective in this bridal metaphor in Eph 5. Christ is the head of the church, which submits to his authority. That all things will submit to the authority of Christ is a view of the future when Christ returns (cf. Phil 2:5-11). But, on the other hand, the marriage is already in existence and there are aspects of a realized eschatology here. On the other hand, the idea of a splendid church (5:27) may imply a future eschatological element is present.
At some point in the future the church will finally be a pure and spotless bride prepared for the bridegroom at the Second Coming (the “wedding supper”). I am tempted to see this as another aspect of the already / not yet tension of Pauline eschatology, but I am not sure that Paul’s topic in Eph 5 is eschatology at all, but rather the purity of the church in the prestent age.
It could therefore be argued that Paul, who took a negative approach of sexual purity (commands not do be immoral, 5:3-7), now adopts a positive argument, “reflect the love of Christ” in sexual ethics (your own partner). The “function” of the metaphor is to get the husbands to see themselves as in some ways an “ecclesial bride,” if Christ and the church are “one flesh,” and covenant loyalty is obvious and required, then the husband ought to have the same level of commitment to their wives.
So Paul does use the marriage metaphor, but he spins in the direction of a ethical teaching on the relationship of a husband and wife in their marriage relationship.