I was wondering what went through between the Apostles and other followers of Jesus' in the upper room on the first Easter Vigil. They were probably crushed by Jesus' death on Good Friday and perhaps were seeking consolation in their thoughts and with each other.
What do we ourselves do when mourning the passing of a loved one? After the tears have dried out, we typically start recalling memorable events of one's life. Particularly those who met Jesus in His public ministry, but also the Apostles, perhaps recalled His baptism, His first miracle, His teaching, His transfiguration, His gift of Himself to us...
On the other hand, there was one woman in the upper room who most likely had different recollections: Mary, as she had just experienced the last and greatest of sorrows. Which mother wouldn't be recalling her child's conception, pregnancy, birth, dedication to God, maturation?
It seems to me then that by saying the Luminous Mysteries on Saturday, I'm putting myself in the upper room with the Apostles. And if instead I say the Joyful Mysteries, I'm letting my Mother open her heart to me.
Jesus called the Apostles to follow Him, but no one followed Him so perfectly as His mother, even before knowing Him. Yet, all of them found unspeakable joy on Easter Sunday at His resurrection and then were filled with the Holy Spirit by the Son of God.