If you receive an invitation to a wedding, but cannot attend, you can still send expressions of happiness to the bride and groom. R.S.V.P. in a timely way, your regrets, your congratulations and suggest getting together with the couple after the wedding. Write from the heart and you will leave an impression that the bride will carry with her on her special day.
When you know you will be unable to attend a wedding, let the bride know as soon as possible. Express your sincere apology that you cannot celebrate the couple's joy. Use words that reflect your personality and communicate how much you wish you could attend.
In addition to your regret, express your happiness for the couple with a brief, but heartfelt congratulatory note. Think about what you would say in the reception line. Your note and the brief expression of joy in line should take about the same amount of time. Don't gush, but be sincere. You might quote a couple of brief lines from a poem or write a few lines that make a personal reference to the bride and the groom.
Let the bride know you will be thinking about her and the groom on the wedding day. Include a brief note that you plan to take a few moments at the time of the wedding to send a prayer for the couple's continued joy.
Even though you cannot attend the wedding, include a suggestion to get together after the wedding. Write that you will call after the wedding or honeymoon. Suggest taking the couple to dinner or getting together to hear all about the wedding and to see the video.