When couples are near a milestone anniversary in their marriage, e.g. – end of first year, 10th or 25th anniversary, or when they have come together after a major event in their lives, it can be appropriate to mark the occasion with a ceremony.
The event may be just the couple in a private setting….or the couple with their original bridal party….or something bigger and grander at home or elsewhere.
An experienced celebrant will listen carefully to the couple’s ideas, especially why they are renewing their vows, and guide them in creating a ceremony appropriate for them – choice of vow (do they have a copy of their original vow?), reading(s), ring(s), any children involved, and so on.
...Your professional contribution truly reflected the significance of celebrating the renewal of our wedding vows. - Linda & Gregor
The ceremony is sometimes staged as a surprise to the guests who thought they were "just coming to a 40th birthday party". Sometimes the wife or husband arranges it as a surprise for the other, in this case, the celebrant has a critical role to ensure that at the time of the ceremony the ‘surprised party’ does not feel coerced to proceed.
Vow renewals are not a legal ceremony, rather a milestone ritual of significance to the couple.