First of all, the preamble is important because it provides a more concrete explanation of why this bill was introduced. Basically, it has an interpretive value for courts that may need to study this piece of legislation. The part that talks about the persons appointed with the approval by resolution of the Senate, the House of Commons or both Houses of Parliament is the cornerstone for determining the positions that must be bilingual. I think the preamble plays a major role in helping to interpret what an officer of Parliament is. In the future, if there are new officers of Parliament, this can help to determine which positions to add.
On March 26th, 2013. See this statement in context.