Biblical title of honor, literally "father," used as an invocation of God, from Latin abba, from Greek abba, from Aramaic (Semitic) abba "the father, my father," emphatic state of abh "father." Also a title in the Syriac and Coptic churches.
It is used in the New Testament three times (Mark xiv. 36, Rom. viii. 15, Gal. iv. 6), in each instance accompanied by its translation, "Abba, Father," as an invocation of the Deity, expressing close filial relation. Either through its liturgical use in the Judeo-Christian church or through its employment by the Syriac monks, it has passed into general ecclesiastical language in the modified form of abbat or abbot .... [Century Dictionary]
1830, "a decisive blow" (also, figuratively "a conclusive argument"), fanciful formation from sock (v.1) "hit hard," perhaps via a comical mangling of doxology, on a notion of "finality." The meaning "something exceptional" is attested from 1838.
Sockdologizing likely was nearly the last word President Abraham Lincoln heard. During the performance of Tom Taylor's "Our American Cousin," assassin John Wilkes Booth (who knew the play well) waited for the laugh-line:
Don't know the manners of good society, eh? Well, I guess I know enough to turn you inside out, old gal—you sockdologizing old man-trap.
Amid the noise as the audience responded, Booth fired the fatal shot.