Fifty days after Firstfruits is the Feast of Pentecost, which pictures the formation of the church. At Pentecost, the Jews celebrated the giving of the Law, but Christians celebrate the giving of the Holy Spirit to the church.

The Feast of Firstfruits took place on the day after the Sabbath following Passover, which means it was always on the first day of the week. (The Sabbath is the seventh day.) Jesus arose from the dead on the first day of the week and “became the firstfruits of them that slept” (1 Cor. 15:20). Now, if Pentecost was fifty days later—seven weeks plus one day—then Pentecost also took place on the first day of the week. Christians assemble and worship on Sunday, the first day of the week, because on that day our Lord arose from the dead, but it was also the day on which the Holy Spirit was given to the church.

Acts 2:1-6