Zerwick writes: "The repetition of the article
distinguishes two coordinated notions, while on the
contrary the use of but one article before a number of
nouns indicates that they are conceived as forming a
certain unity, if not as identical" (Biblical Greek
Illustrated by Examples. Roma: Editrice Pontificio
Istituto Biblico, 2001. Pp. 59-60.
However, while there are clear examples such as 1
Thess 2:12 that seem to support this grammatical
principle, 2 Cor 8:4, 19, 24; 9:13; 1 Pet 4:14 seem to
militate against it. Zerwick adds:
"On the other hand, we are perhaps warned not to
insist too far by such examples" as those cited above.
See Zerwick, ibid., p. 60.