Sheep-Goat Judgment

What is the "Sheep-Goat Judgment" that Jesus discusses with His disciples at the end of the Olivet Discourse? He tells His followers that those who provide help to "the least of these" will enter His kingdom, and those who ignore "the least of these" will be sent to eternal punishment. Isn't this salvation by works? Faith is not mentioned at all in the passage. Does Jesus contradict the Apostle Paul who wrote "for by grace you are saved through faith; not as a result of works, lest any man boast"?