It's not "mystical" significance, but there is significance.
For example, the Sunday readings work through one of the synoptic gospels each year in the three-year cycle, with readings from John interspersed.
The gospel readings basically tell the story of Christ's life from before the beginning to after the end, but there are a couple of parallel "timelines". One starts with the first Sunday of Advent and ends after Easter; the other starts after the Christmas season and continues until Advent.
The first one points to the resurrection of Christ; the second points to the resurrection of all men at the last day.
Each week, the OT reading is the prophetic foreshadowing of the Gospel reading. This is true except during the Easter season, when the first reading tells the story of the infant church from Acts.
Trust me, the selections are "jumbled" and were carefully thought out over years by solid Scripture scholars.
Should have been: Trust me, the selections are not "jumbled"