Although it can be useful for a preacher (especially a young preacher) to write out the sermon in full, there are sound reasons for the preaching itself to be from notes, rather than from a full manuscript.

Preaching from a full manuscript:-

1. usually leads to ‘bubble preaching’.  The preacher has prepared every word of the message, and that is needed now is to read it off the paper.  Eye contact with the audience, and rapport with them, will be severely restricted.
2. over-emphasises content over delivery.  Of course, the quality of what we deliver to our hearers is vital.  But we must not neglect the quality of how will deliver it.  And this will almost certainly suffer if we are tied to our notes.
3. slows a preacher’s development.  There will be many occasions – in pastoral counselling, for example – when the preacher will have to speak extemporaneously.  Preaching from a full manuscript will slow down the process of learning that skill.
4. misunderstands the differences between written and oral communication.  They differ in many ways – pace, style, cadence, and even vocabulary.  It is very difficult (and probably not a good use of the preacher’s time to try) to write a manuscript that lends itself to an oral style.  The speaker should speak, not read.

These limitations do not mean that it is impossible to preach effectively from a full manuscript, but they do indicate that notes (even if they are fairly detailed notes) are the way to go.