When I spoke of over-spiritualizing, the meaning was in relation to painting everything with allegory to the extent that spiritualizing it all only leads to some making it say whatever they so desire for the scriptures to say in order to make it conform to their personal beliefs.
MM
In the context of the gospel, the historical events depicted in the Bible serve as allegories representing spiritual truths. Allegory is the means by which spiritual truths are revealed and conveyed by the narrative, yet only the spiritual is the true, and the allegory, reflections, and images of it, have no spiritual efficacy of themselves. If, as we are told in Gal 4:22 - 4:26, that Abraham had two sons, which sons formed as allegory the basis of the entire gospel for the two covenants, how then could anything else in the gospel that was built upon them - which almost everything else in it was - themselves also be anything other than allegory?
Therefore, given that the spiritual is the basis of, and is behind the gospel, it would be impossible to "over-spiritualize it" (whatever that may imply), however, to under-spiritualize it, would definitely be a possibility and a very great danger: biblical truth and sound doctrine are discerned only through the comparison of spiritual with spiritual as we are told in 2 Co 2:13, not by the comparison of the historical/earthly with historical/earthly given that the latter comparison can yield only earthly wisdom, not spiritual wisdom.
[Gal 4:22-26 KJV]
22 For it is written, that
Abraham had two sons, the one by a bondmaid, the other by a freewoman.
23 But he [who was] of the bondwoman was born after the flesh; but he of the freewoman [was] by promise.
24
Which things are an allegory: for these are the two covenants; the one from the mount Sinai,
which gendereth to bondage, which is Agar.
25 For this Agar is mount Sinai in Arabia,
and answereth to Jerusalem which now is, and is in bondage with her children.
26
But Jerusalem which is above is free, which is the mother of us all.
[Heb 8:5 KJV]
5 Who serve unto the
example and shadow of heavenly things, as Moses was admonished of God when he was about to make the tabernacle: for, See, saith he, [that] t
hou make all things according to the pattern shewed to thee in the mount.
[Heb 9:23-24 KJV]
23 [It was] therefore necessary that
the patterns of things in the heavens should be purified with these; but the heavenly things themselves with better sacrifices than these.
24
For Christ is not entered into the holy places made with hands, [which are] the figures of the true; but into heaven itself, now to appear in the presence of God for us: