In the second place, the oblation "of the first fruits", that is, of the beginnings of the produce, is commanded. And this, if you remember well, the law commands to be done on the day of Pentecost. In which a "shadow" plainly was given to them, but for us the truth was reserved. For on the day of Pentecost, when the sacrifice of prayers had been offered, the Church received the first fruits of the coming "Holy Spirit" of the Apostles.
Source: HOMILIES ON LEVITICUS 2