Here is the answer of so-called Christians :
w04 9/15 p. 28
Questions From Readers
Why were Israelite men permitted to marry captive foreign women when the
Mosaic Law commanded that no marriage alliance be formed with
foreigners?—Deuteronomy 7:1-3; 21:10, 11.
The reason this was allowed had to do with special circumstances. Jehovah had
commanded the Israelites to demolish the cities of seven nations in the land of
Canaan, killing all their inhabitants. (Deuteronomy 20:15-18) In the case of
other nations, the only likely adult survivors were captured virgin women.
(Numbers 31:17, 18; Deuteronomy 20:14) An Israelite man could marry such a
woman, but only if she took certain measures.
Concerning the steps such a woman was required to take, the Bible states: “She
must now shave her head and attend to her nails, and remove the mantle of
her captivity from off her and dwell in your house and weep for her father and
her mother a whole lunar month; and after that you should have relations with
her, and you must take possession of her as your bride, and she must become
your wife.”—Deuteronomy 21:12, 13.
A captive virgin whom an Israelite wanted to marry was to shave her head.
Cutting off the hair was an expression of mourning or distress. (Isaiah 3:24) For
example, when the patriarch Job lost all his children and property, he cut the
hair off his head as a sign of mourning. (Job 1:20) The foreign woman was also
to attend to her nails, perhaps ‘paring her nails close’ so that even if they were
colored, her hands would not look attractive. (Deuteronomy 21:12, Knox) What
was “the mantle of her captivity” that the captive woman was to put aside? It
was customary for the women of pagan cities who were about to be conquered
to dress in their finest clothing. They did this in hopes of winning the favor of
their captors. Such apparel had to be set aside by a captured woman in
mourning.
A captive woman who was to be the wife of an Israelite man was to mourn for
her dead loved ones for one lunar month. The destruction of the defeated
cities was to be so thorough that all her former family and social ties would no
longer exist. Since the Israelite soldiers would have destroyed images of her
gods, her objects of adoration would be gone. The month of mourning also
served as a period of purification during which a captive woman would free
herself of all features of her past religious devotion.
The situation was different, though, in the case of foreign women in general. In
this regard, this principle applied: “You must form no marriage alliance with
them. Your daughter you must not give to his son, and his daughter you must
not take for your son.” (Deuteronomy 7:3) What was the reason for this
restriction? Deuteronomy 7:4says: “For he will turn your son from following
me, and they will certainly serve other gods.” The prohibition, then, was for the
purpose of protecting the Israelites from religious contamination. However, a
foreign woman in the circumstances described at Deuteronomy 21:10-
13 presented no such threat. All her relatives were dead, and images
representing her gods were destroyed. She had no contact with practicers of
false religion. An Israelite was allowed to marry a foreigner under such
circumstances.