ChristianAnswers.Net WebBible Encyclopedia
Quotations from the Old Testament in the New, which are very numerous, are not made according to any uniform method. When the New Testament was written, the Old was not divided, as it now is, into chapters and verses, and hence such peculiarities as these:
In general, the New Testament writers quote from the Septuagint (q.v.) version of the Old Testament, as it was then in common use among the Jews. But it is noticeable that these quotations are not made in any uniform manner. Sometimes, e.g., the quotation does not agree literally either with the LXX or the Hebrew text. This occurs in about one hundred instances. Sometimes the LXX is literally quoted (in about ninety instances), and sometimes it is corrected or altered in the quotations (in over eighty instances).
Quotations are sometimes made also directly from the Hebrew text (Matt. 4:15-16; John 19:37; 1 Cor. 15:54). Besides the quotations made directly, there are found numberless allusions, more or less distinct, showing that the minds of the New Testament writers were filled with the expressions and ideas as well as historical facts recorded in the Old.
Besides quotations in the New from the Old Testament, there are in Paul's writings three quotations from certain Greek poets, Acts 17:28; 1 Cor. 15:33; Titus 1:12. These quotations are memorials of his early classical education.