It seems to me that Friday and/or the 13th is an omen of the ultimate "bad luck"
of the devil.
And it is his super-sly subversion of truth that has enabled him to keep that from
being publicly recognized.
All the 12 Apostles with Our Lord numbered 13.
The 12 Articles of the Creed, together with the one you'll find prominently in the
Athanasian Creed (an authoritative Creed of the Church), namely, extra
ecclesiam nulla salus, makes 13 articles Catholics must hold to be in the Church,
outside of which, of course, there is no salvation to be found.
Once Our Lord ascended into Heaven, perhaps the devil thought that finally, he
would have a chance to "get even." But alas, only 9 days later, with the Blessed
Virgin Mary keeping them safe from harm with her Immaculate storehouse of
graces, they burst forth from the womb of the Upper Room, transformed into
Personally Infallible Generals on the march, looking for their respective armies.
And how many does that make? 12 Apostles plus Our Lady = 13 formidable
obstacles to the dismal reign of the prince of this world.
And last but not least, the 13th of every month is the day we can reasonably set
aside to recall the great grace of the intercession of Our Lady of Fatima on 6
consecutive months in 1917, from May 13th to October 13th.
These are all really bad things for the devil's agenda: bad "luck" for him!
And Friday is the day he got snookered big time, when his kingdom was defeated
in eternity, the day Our Lord made the ultimate Sacrifice on the Cross.
Therefore, Friday the 13th is really bad luck for the devil.