It would be hard to imagine that these little rules that are listed throughout the Missal would be anything more than boring technical details. Although it may be hard to believe, I was once deeply moved spiritually by a rubric. It was actually from the old Sarum Missal (from which the Divine Worship Mass is derived). In summary, the rubric said, "the priest shall pause here and remain silent, but not too long for danger that the devil may tempt his mind to wander". Wow!
Ponder that for a minute. "That the devil may tempt his mind to wander"; those are not merely "technical details" they are the substance of spiritual warfare. We are certainly a people whose minds are prone to wander. After all, we are immersed in distractions and any little thing makes our minds wander away from the task at hand (as I have written about many times before). Every one of us is subject to various distractions, and we all have to find proper ways to deal with them (which does not mean ignore them).
Yes, priest's minds do wander during Mass as well. It is a bit less common since we are so focused on all of the aspects of the Mass (at least, we are supposed to be focused!). Yet, things can happen that will pull us away. I recall one time when I was still thinking about a recent death in the parish, and suddenly during the Eucharistic Prayer I thought (just for a moment) about his widow, who was seated just a few pews back from the front, and whether she was doing OK. That is all it took: one thought, a quick glance, and then I lost my place on the page of the Missal. That made me stumble in my words as I was looking for the right place. Although it may seem like a small thing, the reverence of the Mass was impacted at that moment because I got distracted (even with something truly important).
We all need to view what we do during the Mass in that same way. Being cautious that our minds may be tempted to wander is not a petty thing, and there is nothing scrupulous about being concerned to stay focused on Christ during the Holy Sacrifice. Yet, that is the very thing that the evil one wants to do to us: make us lose focus. It is almost ironic that there are so many people today who drive distractedly (looking at their cell phones for one reason or another) and appear to think nothing of it, or how it impacts their behavior in other areas of life. If it is dangerous to our physical well being to get distracted while driving, it is all the more dangerous to our spiritual well being to be distracted while worshipping our Almighty Creator.
Let us prepare our hearts and minds before we enter the Church, and when we do, let us pray again for help to be attentive to the holy event that is going on in our very presence. Parents, work to help your children to remain focused -- it can be done even with the little ones (if you control the amount of distractions children are exposed to outside the Mass, it makes it easier for them to focus while in the Mass); I have seen it firsthand (more than once). If the devil cannot keep you out of the Mass itself, then he will do everything he can to keep your mind and heart elsewhere. Remember:
"Be sober, be watchful. Your adversary the devil prowls around like a roaring lion, seeking some one to devour. Resist him, firm in your faith (1 Peter 5:8)."