Although you may know what you want to express in your speech the format of the presentation may not provide you with a pattern that allows you to see in advance how the speech actually will finish up.   There are many formats you can choose to follow.

You could write your text out in full then you would memorize it and then "read" the speech, then you could submit it to cards and make a card presentation.   This format only allows you to "wing it" from the notes.   Neither one of these formats provides you with the structure or confidence you require to deliver an effective presentation with confidence.   There are many reasons why the format of a speech is important.   The format must provide you with the information that is accurate and complete.   For instance, when quoting others you must be sure of the accuracy of your statements.   When you decide to use a card presentation a proper and complete rehearsal is important.   Then of course you must be confident of your ability to deliver the speech effectively and accurately.   You also must be able to depend on the format to be useful with any speech at any time.