"It was right that we should make merry and be glad, for your brother was dead and is alive again, and was lost and is found."
There are some very appropriate times to rejoice, and celebrate. At the top of this list is the salvation of a soul. The older brother (in this "Prodigal Son" narrative) refused to party with his father, because he (the older son) could not accept the concept of grace and forgiveness. He was all about works, and self-righteousness.
May we be very glad when God calls sinners to Himself, through the gospel of Christ; and may we renew our own love to and amazement at God (who does such wonderful things).
[Puritan quote of the day: "Love to Jesus Christ and believing in Jesus Christ fills the souls with joy and glory in this life." --Christopher Love, in his sermon on Gal. 5:17]