Please note the Holy Father's collar which is not framed by the cassock:
Please note his sleeve at the Rite of Sprinkling, see a cassock sleeve underneath?
Okay I notice things! Why? I do not know, but when something is different I notice it intuitively and then look more closely and see what it is that is missing.
I could tell by looking at his neck and how the amice showed a collar without a cassock frame. I could tell by the cuffs where the white shirt without cuff links showed under the alb, but not the sleeves of the cassock, which is normally quite visible. I could tell by looking at the hem of the alb that only showed the black pants and orthopedic shoes that the Holy Father had on underneath, no additional cassock which is normally a bit longer than the alb.
Today Pope Francis did not wear the papal cassock under the alb. Maybe it was too hot and maybe he had a long day ahead. Certainly he did have a long day awaiting with the historic Interfaith Prayer Service with Christians, Jews and Muslims each offering prayers in their own traditions for the peace of Israel and Palestine, peace in the Middle East where a violent conflagration of worldwide proportions could easily occur.
Of course I have a confession. I do not wear a cassock as street clothes even on Church property. I do wear a cassock and surplice for some liturgical functions and certainly I did when I was the Diocesan Master of Ceremonies.
On a few occasions I have worn the cassock under the alb for Mass in both forms, but in both forms I usually do not. I find it bulky and too hot.
Did you notice the Holy Father not wearing the papal cassock under his alb during the Pentecost Mass? This is the first time I've noticed it and is not a regular occurrence. Does it matter if one, even if Bishop of Rome or any bishop or any priest or deacon, does or doesn't wear his cassock under the alb for Mass?