Terumah opens with God telling Moses to instruct the People of Israel to bring Him gifts. Which is pretty much how I like to start any good story. Bring me gifts. Please. Teasing aside, God tells Moses to impart the news to the people that they should bring gifts to be used in the building (and beautifying) of the Mishkan - the Tabernacle that will hold the Ark in which God will dwell. The gift offerings can be divided into seven categories: metals (gold, silver, and copper), dyed yarns, fabrics, timber, oil, spices, and gems. Surely some are to be used to build the actual structure of the Tabernacle, but most are to be used to adorn it, to beautify God's (future) home.
There is a principle in Judaism called "Hiddur Mitzvah" - glorifying the mitzvah, adding an element of beauty to it. Rabbi Zera in the Talmud [Bava Kama 9b] says, "In keeping with the principle of Hiddur Mitzvah, one should be willing to pay even one-third more [than the normal price]." It is not enough to fulfill the mitzvah itself, but one should go out of their way to add to it, to make the fulfillment of it beautiful. Surely one could find (or make!) a cheap, flimsy menorah with which to light their Chanukah candles. But have you ever seen a Jewish home without at least one beautiful, ornate Chanukah Menorah? Of course not. We have elevated and beautified the mitzvah of lighting the Chanukah candles by purchasing intricate, artistic candle-holders and placing in them hand-dipped, colorful candles.
This is the same idea behind God requesting these gifts from the Israelites. God's home, sanctuary, and dwelling place should be adorned in a way that is worthy of the Shechinah, God's Presence. How the Israelites "decorated" God's home was a manifestation of their confidence in God. A beautiful home with priceless gems, expensive fabrics, and the best wood available sends a very different message than a plain wooden structure. We use the same logic with our Valentine's Day (or anniversary, birthday, housewarming, etc.) gifts. We know that these gifts send a message to the recipient, and, assuming we like that person, we want to give them the very best we can.
God instructs Moses to accept gifts on His behalf, "from every person whose heart so moves him". This was a voluntary gift-giving opportunity. It was not a tax imposed on the people, but rather an opportunity for them to show God how much they cared. How have you shown God how much you care lately?