Modern critics pronounce this as being "a difficult and certainly corrupt passage"; but it is only elliptical.
make one? = make [of twain] one flesh? Ref to Pentateuch (Gen_2:24). App-92.
Yet had He, &c. And therefore could have made more than one wife for Adam.
spirit. Hebrew. ruach.App-9.
And wherefore one? And what [did] that one [Abraham] who [was] seeking a seed of (or from) God? Hebrew. zera' (as in Gen_21:12; see note there). The logical Ellipsis' must be further supplied: "Was Abraham faithless to Sarah and did he ill-treat her when he took an additional wife? How mach more ought ye to be faithful to your wives? "
one. Refers to Abraham. See Isa_51:2. Eze_33:24. Supply the verb "do", as in Ecc_2:12, and as in Jdg_18:8, from Mal_2:18.