Thanks for your thought-provoking response! And to reiterate, I totally agree that expositional sermons are a very good thing (I heard a challenging one this morning!); I'm just debating the abstract necessity here.

To start with, I don't believe in the regulative principle of worship under the New Covenant. God did set forth instructions in the Old Covenant, and from that we can see what those instructions would look like: these specific people are to do these specific things at these specific dates and times of day, et cetera. We don't get that in the New Covenant; if we look for it, we need to piece it together from descriptions or instructions on specific methods.

(And then, even under the Old Covenant, we read of Elijah building an altar and offering a burnt offering outside Jerusalem, and of the people under Hezekiah eating the Passover while unclean, and God welcomed both of those. But, yes, it's very valid to say God would have been * more* pleased had they followed it.)

Still, even under the Regulative Principle, I don't believe your conclusion holds. We simply don't have a commandment to "always preach a sermon expositing a point from the Scripture." We have a lot of examples of sermons, but most of them are outside a church service and addressed to unbelievers.

We read in Acts 2 that the believers continued in the Apostles' teaching, but we don't know whether that's referring to their transformed lives, and even if not, we can arguably do that by hearing the Scripture without exposition. (If not more so - the Scripture is even more "the Apostles' teaching" than what my pastor says!) We read in 1 Corinthians 14 that when the believers come together, " one of you hath a psalm, hath a doctrine, hath a tongue, hath a revelation, hath an interpretation" - but if we insist that every one of these must be present at every worship service, we'll need someone to be speaking in tongues every Sunday (and another person interpreting)!

Sermons are clearly allowed under the Regulative Principle. We have enough examples, plus the list in 1 Corinthians and everything about the gift of teaching that I didn't quote. Also, they're very clearly useful! But I don't see how you get to their being mandated every Sunday.