Relationally, engagement is an unstable time. Prior to engagement, only loose expectations form the relational bond. Both parties know that they can end the relationship for a variety of good reasons (there are, of course, also plenty of bad reasons, but the point is that good reasons exist). After marriage, lifelong promises bind the couple in a security that allows difficult issues to be faced with confidence that the other has publicly promised to keep holding and loving in whatever circumstances or difficulties arise. But during engagement, there exists the somewhat strange circumstance of a private promise that a public promise will be made. There exists during this period a rapidly closing door out of the relationship and this itself can bring added stress and uncertainty to the relationship. Limiting this stressful period to a definite (and relatively brief) period of time is healthy. Open-ended engagements seem either somewhat pointless or somewhat cruel. Once the decision to get married has been made, then all that is required is some time to prepare for the solemnity of the promises to be undertaken and to arrange the details of a wedding - which brings us to the second benefit of brief engagements.
Practically, the wedding preparation will expand to fill the time available. The longer that is given to this process, the more likely the celebration will grow into an all-consuming beast. Better to acknowledge that, while a day of great seriousness and great joy, a wedding is but another day that the Lord has made, and doesn't require great debts to be shouldered or unrealistic expectations (from whatever source) to be appeased. If present finances are insufficient to pay for the scale of expenses expected, then it is far better to humble one's expectations than delay the date. The point of the day is the making and celebrating of promises. All else is optional.
That said, I doubt the Prince and his family are accustomed to too much humbling of expectations. Yet humility befits even (perhaps especially) a future king.
Image by Scott Callaghan.