Yom Kippurim  יוֹם כִּפּוּרִים

On the tenth day of the seventh month is the Day of Atonement יוֹם כִּפּוּרִים Yom Kippurim. The Day of Atonement is the culmination of the ten days of repentance עֲשֶׂרֶת יְמֵי רַחֲמִים Aseret yemei rakhamim. On this day we pray to God for the forgiveness of all our sins.

The Day of Atonement begins on sunset on the ninth day of the seventh month. The Day of Atonement ends with sundown on the tenth day of the seventh month.  

On the day of Atonement it is our duty to keep a strict fast tzom צוֹם, we deny ourselves food, drink and all other pleasures and benefits. We sanctify this day by repentance and by prayers for forgiveness of all of our sins.

The evening prayer on Yom Kippurim תְּפִלַּת עֶרֶב יוֹם כִּפּוּרִים Tefilat erev Yom Kippurim begins at evening after sunset. The  morning prayer of Yom Kippurim תְּפִלַּת בּקֶר יוֹם כִּפּוּרִים Tefilat boker Yom Kippurim begins in the morning and lasts until sunset. The evening and morning prayers take place in the kenasa.

The Day of Atonement is the most important of all holidays, it's the Shabbat of festive rest שַׁבָּת שַׁבָּתוֹן Shabbat Shabbaton, it is also called the Shabbat of Shabbats, all work is forbidden on this day.

Howbeit on the tenth day of this seventh month is the day of atonement; there shall be a holy convocation unto you, and ye shall afflict your souls; and ye shall bring an offering made by fire unto יהוה. And ye shall do no manner of work in that same day; for it is a day of atonement, to make atonement for you before יהוה your God. For whatsoever soul it be that shall not be afflicted in that same day, he shall be cut off from his people. And whatsoever soul it be that doeth any manner of work in that same day, that soul will I destroy from among his people. Ye shall do no manner of work; it is a statute for ever throughout your generations in all your dwellings. It shall be unto you a Shabbat of solemn rest, and ye shall afflict your souls; in the ninth day of the month at even, from even unto even, shall ye keep your Shabbat. (3M 23: 27-32)

We will not describe here in detail how prayer on this day must be performed, nor when our prayer is worthy of God, nor when it will be accepted by God.

If we repent sincerely during this day, our sins against God will be forgiven, but for forgiveness of sins against our neighbors it is necessary to become reconciled with our neighbours before the beginning of this day to compensate them and ask them for forgiveness Mekhilah מְחִילָה. On this day, we are required to forgive all those who offended us in any way, the same as other people forgive us our transgressions against them.

Here the prophet Isaiah speaks about those who think that they get rid of their sins only by fasting, without reconciliation with neighbors:

Is such the fast that I have chosen? The day for a man to afflict his soul? Is it to bow down his head like a bulrush and to spread sackcloth and ashes under him? Wilt thou call this a fast and an acceptable day to יהוה? Is not this the fast that I have chosen? To loose the fetters of wickedness, to undo the bands of the yoke and to let the oppressed go free, and that ye break every yoke? Is it not to deal thy bread to the hungry and that thou bring the poor that are cast out to thy house? When thou seest the naked, that thou cover him, and that thou hide not thyself from thine own flesh? Then shall thy light break forth as the morning, and thy healing shall spring forth speedily; and thy righteousness shall go before thee, the glory of יהוה shall be thy reward. Then shalt thou call, and יהוה will answer; thou shalt cry, and He will say: Here I am. (Isa 58:5-9)