the in-gathering of the filings

There's a great metaphor the Ben Ish Hai (Introduction to Parashath VaEra, Year 2) uses to explain what the final resurrection will be like. He explains first that only the Jewish people will be resurrected, and while this does not differentiate them now at this time, when HaShem drops the dew of life on the ground, it will be absorbed only by the dust that was formerly part of a Jewish body, and it will return life to that body.

How will the dew differentiate between Jewish and non-Jewish dust? Here's his example: Imagine someone spread iron filings all over a dark sandy floor. There's no distinguishable difference between the different kinds of dust.. but pull out a magnet and instantly discerning which dust particles are iron filings becomes trivial.

Similarly, when the final resurrection takes place, only then will the different nature of the Jewish People become apparent. This, R' Hayyim explains, is hinted to in the letter vav of the word פדות (pedut) which is not written in the text, but is nonetheless pronounced.

soul survivors

If our soul doesn't spend time learning God's Torah and keeping God's mitzwoth in this world, our body won't rise up in the end of days, in the time of the resurrection. (Ohr HaHayyim, Haazinu)

He learns it out from here: If the heavens [soul] listen to my speech, then the earth [the body after the soul's departure] will hear my voice [when it calls, as the Zohar teaches, in the end of days to awaken the body once more]

a glimpse of the world to come

Out of the three regalim, the three festivals, Shavuot is a one-day affair. The other two are seven days long, and Sukkoth even has a special extra eighth day.

Yet there is a halachah that if someone passes away the day before Shavuot, those who must mourn them essentially do not sit shiva. What's so weird about this? Shiva is named for the fact that it is a seven-day mourning period. When Shabbath falls during the shiva, we don't observe most of the minhagim associated with shiva, because one can't mourn outwardly on Shabbath.

When this mourning period falls before Pesah or Sukkoth, it's understandable that there is no real period of mourning, we are commanded to be happy on the festivals, and these festivals each last seven days in length, which means that there is no time left in which to observe the mourning period.

But what about Shavuot? It's only one day long, so if someone passed away right before Shavuot, why wouldn't the mourners be required to sit for the five days after Shavuot? 

In order to answer this I need to share something with you about the true nature of time and the world to come. The world to come is called a day that is entirely long. What does this mean? Chazal explain in the hidden Torah that in this world, each day vies for it's time in the spotlight and since the days themselves cannot get along and work together, each day shines for twenty-four hours and then ceases, making room for another day to take over. In the world to come, the days dwell together peacefully and so they all shine at once, indefinitely.

From this perhaps we can see how Shavuot is a taste of the world to come and at the same time explain our quandry regarding the halachot of mourners after Shavuot. I would like to say that Shavuot is actually a seven-day festival just like her sister festivals. The difference is that on Shavuot all the days dwell in peace with one another, and so down here in this world, Shavuot is represented as only a single day -- yet when it comes to the laws pertaining to mourning, since Shavuot is the holiday representing the resurrection of the dead, so we count all seven days of Shavuot and negate the mourning period -- just as the ultimate resurrection will render mourning a moot point.