People misunderstand annulments, I believe, because they misunderstand the role of the Church in the sacrament of marriage. In Catholic theology, unlike the other sacraments in which God’s actions through the priest “make” the sacrament happen (Eucharist, Reconciliation, etc), in the sacrament of marriage, the priest is not the agent so much as the witness to what happens: the sacrament itself occurs between the husband, wife and God. The Church doesn’t “confer” marriage, then, but instead stands as a witness to the vows between husband and wife, offering with those present prayer and support for this couple in their vocation. Just as it does not “confer” on the front end, therefore, it does not have the authority to “de-confer” on the back end. The Church cannot take away what it never gave.
Why then, is the Church involved with annulments? Precisely in its role as witness to the marriage. A marriage is only a marriage if during the time of vows, the bride and groom were truly able to “consent” to the covenant, free and unencumbered by external or internal impediments. Using a silly example to make the point, if the bride were pregnant and the bride’s father sat in the front pew during the marriage ceremony, brooding, armed with a gun to make sure the groom “made it right,” it would be reasonable to question whether the groom was ‘freely consenting’ to the marriage. Those present at the ceremony, observing the gun, could certainly verify such doubt!
Similarly, in the annulment process, one or both of the parties asks the Church, as witness to the original vows, to go back and investigate if there was something that impaired their ability to freely consent to each other—even if it appeared the couple made those vows freely. No, it wouldn’t likely be as simple as someone with a gun held to his head! But what if the husband were physically abused as a child? What if a slightly overweight young lady, full of self-loathing, were desperate to “lock down” a relationship with any one who showed her kindness? What if, in the case of an unfaithful husband, there existed a prior pattern in his life of his inability to sustain a commitment to anything (jobs, relationships, schooling, etc)? Might there be reason to believe that in these cases, there wasn't completely free consent?
Of course. And if asked to investigate these marriages as part of the annulment process, the Church would likely find grounds to declare them “null.” But notice this important distinction! The Church isn’t creating something “new” in this declaration, or “ending” what once “was.” Rather, it is simply recognizing what is already true, and has been true from the beginning: these couples were unable, given their impediments, to freely consent to each other. They may have been sincere. They may have been deeply in love. But they didn’t have the true inner freedom to make a life-long vow.
It’s a self evident truth today that many marriages unravel, creating enormous hurt and loneliness. The annulment process is the Church’s attempt to uphold the sanctity of marriage, as per the couple’s vow to each other to be faithful, even in sickness and health, good times and bad”, while at the same time, to recognize the broken-ness in some lives that may make such a promise impossible to make. A woman would not be able to receive an annulment simply because her husband was an adulterer—this is a clear example of a “bad time” they vowed to work through—but the pastoral instinct and realism of the Church allows it to consider whether the defect in character that accounts for his infidelity might indeed have pre-dated his vows to her, opening up the possibility for an annulment, and for this woman, a chance to start over.