Some of the differences between the LXX and MT
crop up in the New Testament (NT), which draws
extensively, but not exclusively, from the LXX.
The meaning of the theological vocabulary of the
NT is interlocked with that of the LXX, especially
in the Pauline writings, and the peculiarities of
the LXX are readily apparent in NT quotations.
Notable is LXX Isaiah 7.14, which promises that a
virgin will be with child. MT Isaiah 7.14 reports
her merely as a "woman" (Heb: almah). Thus the
argument behind Matthew 1.23, which cites this
verse as a prophecy of Jesus Christ, only makes
sense given the reading in the LXX. This, and
examples like it, prompted early Christians to
attribute to the LXX a special status, so as to
safeguard the authority of the NT. As a result,
the differences between the LXX and MT directly
contributed to the distinct directions Judaism and
Christianity took in Late Antiquity.
HH: I don't agree with that interpretation of Isa
7:14 entirely, since I believe that "almah" could
mean "virgin," but he whole paragraph reflects a
widespread academic recognition of the
correspondence of NT texts to the LXX.
HH: Here is an interesting website on the topic by
an admitted non-expert who has nonetheless done
work that shows the basic correspondence of much
NT quotation of OT material to the text of the LXX: