This is something of a dry reading. Vayak'hel is the instructions for the construction of the Tabernacle, while Pekudei is an accounting of the materials used and the assembly of the worship accessories. How to relate this to today's reality, where we have neither Tabernacle nor Temple, and our worship bears little similarity to the priestly rituals prescribed in these chapters?
I looked through some of the interpretations on http://www.torah.org/ and, while these were interesting, most seemed to latch onto a small detail and read into it some greater message. (Check it out -- some cool, thought-provoking stuff!) Then I noticed a passage that several rabbis commented on. I looked it up, and found it right at the beginning of Vayak'hel:
1 Moses then convoked the whole Israelite community and said to them:
These are the things that the Lord has commanded you to do: 2 On six days work may be done, but on the seventh day you shall have a sabbath of complete rest, holy to the Lord; whoever does any work on it shall be put to death. 3 You shall kindle no fire throughout your settlements on the sabbath day.
Only then do the instructions for the Tabernacle-building begin! Rabbi Yaakov Menken suggests one explanation for this, having to do with the importance of Shabbat, that it should not be violated even for the construction of the Temple. However, that still does not answer why these 2 topics are combined in the first place.
As I see it, such juxtapositions are never a coincidence in the Torah. If they are together, then they are connected. And in fact, there is a connection: The Sabbath is a sacred time, and the Tabernacle is a sacred place. The juxtaposition suggests to me that the instructions for constructing the Tabernacle are analogous to how we should observe - or construct - the Sabbath.
Let us count the parallels:
1. Community - The Tabernacle was first and foremost a "Tent of Meeting" - a place for all the tribes of Israel to come and worship as one. The Sabbath is likewise a time for Jews to worship as a community - men, women and children - at a synagogue (Beit K'nesset = House of Gathering).
2. Tzedakah (Charity) - Just as donations were solicited from the entire people for the construction of the Tabernacle, so the coming of Shabbat is often marked by charitable giving, as well as hospitality to Jews who find themselves away from home (but are prohibited from paying for a hotel or for meals on Shabbat).
3. Special clothes - Just as the Kohanim (priests) wore special clothes in the Tabernacle, so we dress up extra nice for Shabbat.
4. Ner Tamid (eternal flame) - Parallel to the Sabbath candles
5. Setting of bread - Parallel to the challah
So, as we observe Shabbat, let the rituals direct our minds towards truly making it sacred time, a temporal temple, as it were. Let us become a Nation of Priests, as we were commanded to be, by donning our "Priestly Vestments" on Shabbat and thus becoming a force for holiness on earth.