Who Will Stand the Test of Time?

Courant, I think you may have missed my point. There are aspects of the human experience that don't change. There are far more aspects of the human experience that do change. Popular music tends to focus on the ephemeral. I'm not sure what Steven Foster, for instance, may have to say to a 24th century man growing up in Scotland, who has never been to either Kentucky or Florida. I'm not sure what he has to say to a 21st century kid growning up in NYC. Schutz on the other hand, offers plenty for those who will listen. The quality of Foster's work is very high. I did not mean to demean his music in any way.
If you prefer, contrast "Rowan and Martins Laugh in" to "the Honeymooners." Laugh-In was of the highest quality, but the subject matter is severely dated. The subject matter of the Honeymooners, on the other hand, is not.
Many people think much of what I say is odd. Nothing new here.

Courant,nothing wrong with Foster and yes he does occupy a significant place in music as it relates to American cultural history.
However, comparing him to H. Schutz, perhaps second only to Bach as a composer of religious music, is like comparing a K-mart bike to a Mercedes S-500 .

Schubert wrote:

"...comparing him to H. Schutz, perhaps second only to Bach as a composer of religious music, is like comparing a K-mart bike to a Mercedes S-500"

No argument, and I agree completely. It appears I need to clarify...

I wasn't trying to defend Foster as much as criticize Brownsfan's using him as a counter-example choice to Schutz.

Essentially, my thought was that using Foster as a counter example was dicey in that, whether you like or can relate to his material, Foster is simply too important, even though he is a much weaker composer compared to Schutz. Foster will stand the test of time simply because of his place in musicology from a strictly historical perspective.

By analogy, F. Scott Fitzgerald during his lifetime earned just under $450,000 (about 10 Million adjusted for inflation). Source: http://theamericanscholar.org/living-on-500000-a-year/#.UWEqHldFIvo . In contrast Stephen King has sold 350 Million books and is worth $400 Million. Source: http://www.celebritynetworth.com/richest-celebrities/authors/stephen-king-net-worth/

My thought was that Brownsfan needed to use a counter example who was more of a musical equivalent of Stephen King who, if he's lucky, will be a curiosity in 400 years. Possibly someone like Elton John or Barry Manilow would have been better choices.

In contrast to "Barry Manilow", Foster was more the "Irving Berlin" or "John Lennon" of his day, and will be remembered.

Courant,
It does not appear that my statement and yours with respect to Foster's music are all that far apart.

"Most popular music describes a window in time. Once that time is past, the music becomes a relic that is at best a curiosity."

"Foster will stand the test of time simply because of his place in musicology from a strictly historical perspective. "

My perception is that the OP was not asking about music that would survive to be of historical or academic interest.

Ralph Vaughn Williams (along with many already mentioned).
Mapman - WHAT! no Rolling Stones?

Rok2id - in a future I'd prefer to experience, no one will recall Lady Gag Me or stuff by Tupak etc etc etc etc.