As part of a congratulatory message for an engagement, the writer can express joy on the happy occasion, wish the couple all the best and offer to help in any way that is needed. A short poem or verse from a religious book can be included in the message.
The writer can tell the couple how perfect they are for each other. Express joy that the relationship has progressed to this level and that now they are officially an engaged couple. Write a few personalized lines about how the unique personalities of the couple, when combined, make their relationship and love so special and beautiful. The writer can tell the couple how happy and excited he or she is for them and how eagerly they are looking forward to the wedding. Share a few memories that contributed significantly to moving the relationship forward to the point of an engagement.
Offer to help in any way that the couple may need. Wish the couple every joy and blessing for the wedding and for the rest of their married lives. The writer can include a quote, a few lines of poetry or a relevant verse or portion from a religious book to make the engagement congratulations message more memorable.