Why do we hang ornaments on trees? Certainly to "dress" them up, but long ago, people would hang apples on their trees. Since fruit often grows on trees this makes sense. So the ornaments can remind us of another type of fruit: the fruit of the Spirit.
"The fruit of the Spirit is love, joy, peace, long-suffering, kindness,
goodness, faithfulness, gentleness, self-control." -- Galatians 5:22