Yoma, Chapter 2, Mishnah 4. The Mishnah now turns to the last two lotteries - the third and the fourth.
The Third Lottery - the Ketores:
The third lottery was held for the ketores (incense), and the announcement was made: "Chadashim laketores, bo'u vehafisu" - those who are new to the ketores, come and take part in the lottery. In other words, whoever had not yet had the merit of offering the incense should come and join.
Why specifically those who were new?
Because they made a point of not repeating with someone who had already merited offering the ketores. Offering the incense carried a special quality, something like a charm, that whoever merited it would be blessed with wealth, and therefore they wanted to spread that blessing among everyone.
The source of this blessing is in Moshe Rabbeinu's blessing to the tribe of Levi, from whom the kohanim descend: "Yasimu ketorah b'apecha" - they shall place incense before You, and further on "Yevarech Hashem cheilecha" - may Hashem bless your wealth. From this verse we learn that the ketores has the power to make a person wealthy. For this reason they did not want the blessing reserved for one particular person who would do it again and again, and they took care that no one repeat this service.
The Fourth Lottery - the new together with the old:
The fourth and final lottery was "chadashim im yeshanim" - the new together with the old, meaning both those who had not yet performed this service and those who had already performed it. Unlike the lottery for the ketores, here even those who had done it in the past could participate.
This lottery was for "mi ma'aleh eivarim min hakevesh lamizbe'ach" - who brings the limbs up from the ramp to the altar. Our Tanna holds that the very people who brought the limbs up to the ramp were not the ones who brought them up to the top of the altar; rather, new people performed this service, and the lottery was held for that purpose.
In summary: In this Mishnah we learned about the third lottery, which was held for the ketores and only among those who were "new," so that the blessing of wealth contained in it should spread among all the kohanim; and about the fourth and final lottery, held for "the new together with the old" - for bringing the limbs up from the ramp to the top of the altar, by new people.