Romans 9:27-29 — Isaiah also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved:
For He will finish the work, and cut it short in righteousness: because a short work will the Lord make upon the earth.
And as Isaiah said before, Except the Lord of Sabaoth had left us a seed, we had been as Sodoma, and been made like unto Gomorrha.
Verse 27-28 quote from Isaiah 10:22-23 — For though thy people Israel be as the sand of the sea, yet a remnant of them shall return: the consumption decreed shall overflow with righteousness. For the Lord GOD of hosts shall make a consumption, even determined, in the midst of all the land. Referring to the coming Assyrian captivity and end times.
work — should be "word" (Logos) — what the Lord fulfills
Verse 28 — God will cut short the time to preserve the remnant. (The last part of the verse isn't in the best manuscripts.)
Verse 29 quote from Isaiah 1:9 — Except the LORD of hosts had left unto us a very small remnant, we should have been as Sodom, and we should have been like unto Gomorrah.
Sabaoth = Hebrew word for "hosts"
Paul uses Isaiah's prophecy, still unfulfilled, about a remnant of Israel that will be saved in the end times to refer to a remnent saved by grace in this age.
Seed — the believing remnant in the future.