Pentecost fulfilled by the birth of the Church. This is the only time when God required an offering containing leaven. Leaven symbolizes sin. On this occasion, the Feast of Weeks, two loaves were offered, prophetically representing the two members of the newly born Church–Jews and Gentiles. That saved sinners were brought into the Church, could be the possible explanation to the leavened offering. On the day of Pentecost, you can wish your brothers and sisters in Messiah a “Happy Birthday”, commemorating the day the Church was born.