The disciples were celebrating Pentecost, originally a Jewish festival, when the Holy Spirit descended on them and birthed the church. Pentecost, which began as a harvest festival, had come to commemorate the giving of the law. The Book of Ruth became integral to festival worship.
Why Ruth? This short story doesn’t mention the law. Let alone God giving it to Moses. Yet in Ruth’s devotion to her mother-in-law (“Where you go I will go … Your people will be my people …” [Ruth 1:16, NIV]), she fulfills not just the letter but the spirit of the law: loving kindness – all the more remarkable because she’s a foreigner. Boaz, too, demonstrates exorbitant kindness to Ruth.
As Christians celebrate the Spirit bridging differences in Jerusalem, uniting all nationalities by making the gospel message intelligible to all people, we too can remember Ruth’s story. For in it, God unites two enemy peoples for his grand purpose: Boaz and Ruth’s marriage leads to King David and, ultimately, to King Jesus. Today the Holy Spirit continues to unite all categories of people under Christ’s reign for the good of the world.