John Lightfoot on Matthew 1:17

[Fourteen generations.] Although all things do not square exactly in this threefold number of fourteen generations, yet there is no reason why this should be charged as a fault upon Matthew, when in the Jewish schools themselves it obtained for a custom, yea, almost for an axiom, to reduce things and numbers to the very same, when they were near alike. The thing will be plain by an example or two, when a hundred almost might be produced.

Five calamitous things are ascribed to the same day, that is, to the ninth day of the month Ab. "For that day (say they) it was decreed, That the people should not go into the promised land: the same day, the first Temple was laid waste, and the second also: the city Bitter was destroyed, and the city Jerusalem ploughed up." Not that they believed all these things fell out precisely the same day of the month; but, as the Babylonian Gemara notes upon it, That they might reduce a fortunate thing to a holy day, and an unfortunate to an unlucky day.

The Jerusalem Gemara, in the same tract, examines the reason why the daily prayers consist of the number of eighteen, and among other things hath these words; "The daily prayers are eighteen, according to the number of the eighteen Psalms, from the beginning of the Book of Psalms to that Psalm whose beginning is, 'The Lord hear thee in the day of trouble,'" [which Psalm, indeed, is the twentieth Psalm]. "But if any object, that nineteen Psalms reach thither, you may answer, The Psalm which begins, 'Why did the heathen rage,' is not of them," a distinct Psalm. Behold, with what liberty they fit numbers to their own case.

Inquiry is made, whence the number of the thirty-nine more principal servile works, to be avoided on the sabbath-day, may be proved. Among other, we meet with these words; "R. Chaninah of Zippor saith, in the name of R. Abhu, Aleph denotes one, Lamed thirty, He five, Dabar one, Debarim two. Hence are the forty works, save one, concerning which it is written in the law. The Rabbins of Caesarea say, Not any thing is wanting out of his place: Aleph one, Lamed thirty, Cheth eight: our profound doctors do not distinguish between He and Cheth": that they may fit number to their case...

"R. Joshua Ben Levi saith, In all my whole life I have not looked into the [mystical] book of Agada but once; and then I looked into it, and found it thus written, A hundred and seventy-five sections of the law; where it is written, He spake, he said, he commanded, they are for the number of the years of our father Abraham." And a little after; "A hundred and forty and seven Psalms, which are written in the Book of the Psalms [note this number], are for the number of the years of our father Jacob. Whence this is hinted, that all the praises wherewith the Israelites praise God are according to the years of Jacob. Those hundred and twenty and three times, wherein the Israelites answer Hallelujah, are according to the number of the years of Aaron," &c.

They do so very much delight in such kind of concents, that they oftentimes screw up the strings beyond the due measure, and stretch them till they crack. So that if a Jew carps at thee, O divine Matthew, for the unevenness of thy fourteens, out of their own schools and writings thou hast that, not only whereby thou mayest defend thyself, but retort upon them.