Charles Ellicott Commentary Matthew 1:17

"So all the generations from Abraham unto David are fourteen generations; and from David unto the carrying away to Babylon fourteen generations; and from the carrying away to Babylon unto the Christ fourteen generations." — Matthew 1:17 (ASV)

The arrangement of the genealogy into three groups of fourteen generations each was clearly a form of memoria technica (a mnemonic device). The periods covered by these three groups are, it should be noted, of very unequal length, and the actual omission of names in one group makes it possible that the others were treated in the same way.

1. From the birth of Abraham to the birth of David, taking the dates supplied by the received chronology of the Old Testament (BC 1996–1085).
2. From the birth of David to the Captivity (BC 1085–588).
3. From the Captivity to the birth of Jesus (BC 588–4).

There remains the further question of how to reconcile the genealogy given by St. Matthew with that from St. Luke (Luke 3:23–38). This question is best addressed, it is believed, in a short Excursus in the Notes on that Gospel. For now, it is sufficient to note that the difference between the two is, at the very least, strong presumptive evidence that neither Evangelist had seen the other's record.

Otherwise, it is hardly conceivable that one would have introduced such a significant difficulty without a word of explanation. Presumably, each Evangelist copied a document he found, and the two documents were drawn up according to different plans regarding the principles of succession they recognized.