Topic notes, not a full sermon. Structure from the sermon outline page; the material here is what is specific to this subject.
Three texts, three costs
choose one[they pull in genuinely different directions]
Hebrews 11. Enormous scope, easy to preach as a parade of heroes, and its actual ending is that none of them got what they were promised. Preach the ending and the whole chapter changes shape.
Mark 9:14-29. A father says I believe, help my unbelief, and the healing happens anyway. The single most pastorally useful verse on this subject and the one most sermons on faith omit.
James 2:14-26. Faith without works. Costs you comfort and gains you a sermon with an edge, especially in a congregation that has been fed grace without consequence for a long time.
Faith is not certainty
the distinction[this is the whole sermon in most congregations]
Certainty is a state of mind. Faith in scripture is almost always a direction of travel: people who set out, who keep walking, who act on something they have not verified.
That distinction matters because a congregation taught that faith means certainty will treat every honest doubt as a private failure, and will hide it. Which is how people leave quietly.
The trap
avoid this[the prosperity version arrives by accident in ordinary churches]
Faith as a technique for obtaining outcomes. Preachers who would reject prosperity teaching outright still slide into it on this topic, because the grammar is so available: if you had more faith, then.
The cost lands on the person whose prayer was not answered, who now has an explanation, and it is that they did not believe hard enough.
An angle worth taking
if you want it[mustard seed, read properly]
The mustard seed saying is usually preached as encouragement about growth. It is better read as a statement about quantity being the wrong axis entirely. The disciples ask for more faith and are told, in effect, that more is not the unit.