I’ve read in a number of commentaries that say the time period mentioned in Exodus 19:1 is the same as the length of time between Passover (or Firstfruits) and Pentecost. Exodus 19 starts "On the third new moon after the people of Israel had gone out of the land of Egypt …" They left Egypt after the first Passover. Then the law was given three new moons later, or 90 days later (60 in an inclusive count). So how are they getting 50 days? Matthew Henry’s commentary reads, "The date of that great charter by which Israel was incorporated… The time when it bears date (Exodus 19:1) — in the third month after they came out of Egypt. It is computed that the law was given just fifty days after their coming out of Egypt, in remembrance of which the feast of Pentecost was observed the fiftieth day after the passover, and in compliance with which the Spirit was poured out upon the apostles at the feast of pentecost, fifty days after the death of Christ." Am I missing something in Henry’s and others’ computations? — Nick Karastamatis
Tough question. Let’s begin with the translation of the original Hebrew since, as we will see, this affects our understanding of the text. Either "in the third month" (NIV, NAS, NKJV, NAB, NET, LXX, Vulgate, Biblia de las Americas, Luther, Biblia Nuova Riveduta, etc) or "on the third new moon" (NRSV, YLT, Fox, Louis Segond) can work. In fact, the Hebrew chodesh can mean either month or new moon. With the first translation, there appears to be more latitude, as you observe; the second seems to be more restrictive.
Passover took place at a full moon (the one nearest the vernal equinox), not at the new moon. The second translation implies, as you noticed, a span from a full moon to a new moon two months following, which would be two and a half (lunar) months. That’s more than the required fifty days. So I think we should go with the first translation ("in the third month"), not the second ("on the third new moon"). Once again, Passover takes place at a full moon; Pentecost takes place neither at a full nor a new moon.
But what about the three months, or two (counted inclusively)? The key is that from Passover to the Feast of Weeks must not be calculated as beginning on the first of the month. The fifty days can easily span part of one month, all of the next, and part of the third. Enigma solved!
To illustrate, this year (2007), Passover fell on 2 April. But in some years it falls in March; in 2010 and 2013 this will be the case. When it is in March, the next Feast (Pentecost, Shevuoth, or the Feast of Weeks) falls in May, hence "three months." (This is just an illustration; their month of Nissan does not correspond to our month of April; it spans March and April… but you get the idea.)
But then why does it say "in the third month after…"? Because inclusive reckoning was in play. This is not the same as our modern counting system. Today happens to be Tuesday. Yesterday was Monday. But the ancients would say Monday was "two days ago." They count the first and the last item in the series. Similarly, from Tuesday to Tuesday is eight days, not seven, since we must count the first and last days. Not our system, granted, but it is our responsibility as Bible readers to understand what the text meant to those to whom it was given, not to force it into our modern categories of thought.
To expand a little on this, we encounter the same sort of difficulty in trying to understand when Jesus predicted his resurrection would take place: "after three days" (Mark 8:31), or "on the third day" (Matthew 16:21). Which is correct? "Yes" is the answer — they both are. The ancient Hebrews, Greeks, Romans, and doubtless others thought and reckoned inclusively. This meant that, unless "translated" into modern time categories, some of their periods may appear longer than they actually were. Jesus died on Friday and rose on Sunday — "after three days." This is equivalent, as we have seen, to "on the third day."
So "the third month after" need not refer to 90 days, nor even to 60, as long as three different months are spanned. Passover took place in the middle of the month of Nisan. 50 days later brings us through the month of Iyar and into the early part of Sivan. Three months! That’s the nature of inclusive reckoning.
For all these reasons, I have to go with the NAS, NIV, LXX etc, rejecting the reading of the NRSV, YLT, etc. The reading should be: "In the third month after the sons of Israel had gone out of the land of Egypt…" This third month is really our second month. Not all commentaries notice this, and they are the word of man anyway, not the inerrant word of God.
We have thus solved two "contradictions." The first appears to have arisen from some translators, not from the word of God itself. The second is in our heads: we do not relate to the ancient (and very common) method of inclusive reckoning.
As for whether we have a perfect parallel (Exodus : Sinai :: Cross : Pentecost), my answer is maybe. There is certainly a parallel (in terms of sequence and proximity, if nothing else). But I am afraid the text does not allow us to be dogmatic.
Since it is our duty to strive to interpret the biblical text correctly, occasionally we will have to go into uncomfortable places as we get into the heads of the ancient Hebrews. We must learn to think the way they thought if we are to understand the text as they understood it.