A fast day is described as "a day of Divine goodwill." 
One reflection of G-d's favor is the Torah reading of the
Thirteen Attributes of Mercy in the morning and afternoon
services, for these attributes are a manifestation of unbounded
Similarly, the positive nature of a fast day is demonstrated
by the Haftorah in which we are told, "Seek G-d while He may
be found, call Him when He is near." 
The positive influences of "a day of Divine goodwill" are
especially manifest on the Fast of Gedaliah because it is
observed during the Ten Days of Teshuvah.
This period is the time at which the Thirteen Attributes of Mercy
were revealed,  as alluded to in the verse, "Seek G-d while
He may be found...."
Our Sages  offer two interpretations of this verse:
In one, the verse is understood to refer to the Ten Days of
Teshuvah, a time when G-d makes Himself especially accessible
The second interpretation links the verse to communal prayer.
When a community prays together, the virtue of their unity causes
G-d to draw close to man.
Our Sages state that, during the Ten Days of Teshuvah, an
individual's prayer can have the same power as communal prayer.
When an entire community prays together during the Ten Days of
Teshuvah, their prayers reach an even higher level. 
By the same token, the positive influences of communal fasting
are enhanced on the Fast of Gedaliah, because this fast is
observed during the Ten Days of Teshuvah.
Aspiring to Redemption
The unbounded positive influence of a communal fast is linked to
the era when goodness will spread throughout the world, the Era
of the Redemption.
This may be seen in the Haftorah recited on a fast day which
concludes with prophecies to be fulfilled with Redemption, among
them: "And My house will be called a house of prayer for all
In the Era of the Redemption, the positive aspects of the
communal fasts will be revealed because all the [commemorative]
fast days will then be nullified, and, ultimately, these days
will be transformed  into days of rejoicing and celebration.
The Fast of Gedaliah, in particular, is linked to the Era of
the Redemption by the identity of the person for whom the fast
is named, Gedaliah ben Achikam, the governor appointed by the
Babylonians after their conquest of Eretz Yisrael.
According to some opinions, Gedaliah stemmed from the House
of David  and was the last member of that royal family who
commanded authority over Eretz Yisrael.
This links this "day of Divine goodwill" with "the scion of
David,"  Mashiach, who will restore the Davidic dynasty. 
The Fast of Gedaliah is also connected with the Redemption by
virtue of the meaning of Gedaliah's name.
The Hebrew letters of Gedalyahu  form the words Gadol Yud-He,
"G-d is great."
It is during the Era of the Redemption that G-d's greatness will
be manifest throughout the world. 
The mention of Gedaliah in the name of the fast highlights the
positive aspects of this day in yet another way.
The other three fasts connected with the destruction of Jerusalem
and the Beis HaMikdash are named by the Hebrew dates on which the
respective calamities occurred. The name of this fast, however,
recalls a righteous Jewish leader.
"May it Be Nullified Entirely"
There is another aspect of the Fast of Gedaliah that relates to
the Era of the Redemption.
This fast was instituted because the tragic assassination of
Gedaliah extinguished the last embers of Jewish sovereignty in
Eretz Yisrael after the destruction of the First Beis HaMikdash.
According to many commentaries,  this actually took place on
Rosh HaShanah. The commemoration of the tragedy was postponed,
however, so as not to conflict with the festive celebration of
Rosh HaShanah, a day when we should "partake of delicacies and
drink sweet beverages." 
With regard to the postponement of a fast day, there is a
Talmudic opinion  that "Once [the commemoration of a communal
fast] has been postponed, it should be postponed [indefinitely,
Understood literally, this statement expresses the minority
opinion that when a communal fast falls on Shabbos, the
observance of the fast should not merely be postponed until
Sunday (which is the halachah as we practice it), but that there
is no need to fast at all.
However, the Hebrew wording of this expression leaves room for an
extended interpretation, "Once it has been postponed, may it be
utterly cancelled." I.e., a postponed fast is a time when there
is a greater potential for bringing about the redemptive era
during which the misfortunes recalled by the communal fasts will
be nullified entirely.
The fact that the commemoration of the Fast of Gedaliah is always
postponed,  indicates that this day is uniquely empowered to
hasten the coming of the Era of the Redemption, when all the
commemorative fasts will be transformed into "days of rejoicing
and celebration." May this take place in the immediate future.
- Yeshayahu 58:5; see the explanation in Tanya, Iggeres
HaTeshuvah, ch. 2.
- Yeshayahu 55:6.
- See Zohar II, 177a.
- Or HaTorah, Shir HaShirim, p. 1462. This concept is
alluded to in the use of the plural form of the word
"seek." This can be interpreted to mean that "while G-d
is to be found," i.e., during the Ten Days of Teshuvah,
we should seek Him as a united community.
- Yeshayahu 56:7.
- The transformation of these communal fasts depends on
teshuvah, which transforms evil into good.
Teshuvah is not bounded by time. Therefore on the
communal fasts, our people are able to atone for misdeeds
committed in previous generations, even those, like the
assassination of Gedaliah, which were carried out in the
- . Rambam, Mishneh Torah, the conclusion of Hilchos
Taaniyos, based on Zechariah 8:19.
- There are some indications that Gedaliah was related to
the House of David, for it was a Babylonian custom to
appoint relatives of the kings as governors. Even
according to the authorities (Radak and Abarbanel to II
Melachim 25:25), who state that Gedaliah was not related
to the House of David, his murder shares a connection
with that dynasty. Yishmael, the son of Nesanyah, was a
descendant of the House of David. Jealous that Gedaliah
and not he, had been appointed as governor, Yishmael
murdered him. See Sefer HaSichos, 5751, p. 23.
- Daily liturgy.
- See Rambam, Mishneh Torah, Hilchos Melachim 11:1.
- In Yirmeyahu and II Melachim, Gedaliah's name is
sometimes written as Gedaliah (e.g., Yirmeyahu
40:5) and other times as Gedalyahu (e.g., Yirmeyahu 40:11).
- See Rashi's commentary to Tehillim 48:2.
- See the gloss of Radak to Yirmeyahu 40:1.
- Nechemiah 8:10.
- Megillah 5b. See Likkutei Sichos, Vol. XXXIII, the
Seventeenth of Tammuz, 5748.
- Moreover, Rosh HaShanah often falls on Thursday. In those
years, the third of Tishrei, the day when the Fast of
Gedaliah is usually commemorated, falls on Shabbos, and
the fast is postponed further. Thus when the Fast of
Gedaliah falls on Shabbos, the day is an even more potent
catalyst for the Era of the Redemption.