I posed a question to MavPhil; I will not post the answer, just link to it, as it is really only for those who don’t mind a little intellectual push and shove. 
MavPhil and I both share a repugnance for mystery mongering; consequently we both agree that Dr. Kreeft’s statement, so far as it goes, does not warrant confidence. I don’t own that particular book by Dr. K however, so I don’t know whether he goes into more detail about why it isn’t contradictory, or whether he simply stops with an appeal to mystery.
At any rate, I can consistently call you to witness that I (the hyper-orthodox trinitarian doctrinaire) have never once recommended someone believe a mystery that on examination looks contradictory to the examiner. I have consistently said it is better for someone to reject trinitarian theism (and so also trinitarian Christian theism, although someone could in theory accept the former without accepting the latter) so far as they perceive it to be contradictory, than to accept what they perceive to be contradictory.
I have also pointed out that we (even those of us who reject mystery mongering) are going to have to put up with paradoxes of some kind when talking about the sui generis one and only ground of self-existence (and possibly when talking about lesser realities sometimes, too, such as why the position or the speed of an electron can be calculated but not both simultaneously). But the paradoxes ought to be logically clear as such, either inviting resolution later, or else being clear as to why there can be no further resolution and yet for this case the propositions are nevertheless true although they would be contradictory in other cases. (I used to know and understand why it is true that those two variables cannot be simultaneously resolved for electrons, for example; that was long ago in my senior year of high school advanced science, and I don’t recall the details now, but I do recall clearly understanding why at the time.)
Dr. K is a professional philosopher and so ought to be aware of that; but not all professional philosophers are good at everything, or he may be oversimplifying the presentation to be more accessible to his readers.
Thanks for that thoughtful (as always) clarification, JP.
Once you get past duality and have faith, explanations (when it comes to God) become unnecessary. Paradoxes are held together in the heart. As Rumi has stated:
Here you go Dave. I did this myself.
Lost In Love
I am in love and I don’t know with who
Dead to myself as I am lost in You
Drunk in Beauty my heart is made new
Sweet Divine Mystery I’m in love with You
Reason is gone, love’s arrow goes through
Opposites unite as both sides hold true
United with love we are no longer two
Lost in this ocean I’m in love with You