When Loki needs a quick mode of transport to Jotunheim (the land of the giants), he knows exactly where to find it. Freyja has a magical feather dress that allows its wearer to fly like a bird. Freyja's happy to lend it to Loki. In fact, she tells him, she would give it to him "though of silver bright … though 'twere of gold" ("Thrymskvitha," 4.1-2).
Why does Freyja make a point of proving how super-willing she is to lend her feather dress to Loki? Well, it's because she's a Vanir god and Thor is an Aesir god. The Vanir and Aesir once fought a huge war, and Freyja was traded as a hostage to the Aesir gods. Because of that, we might suspect her of harboring resentment toward the Aesir. Her generosity with her feather dress, though, puts her beyond such suspicions. So her willingness to let Loki borrow her dress symbolizes her cooperation with Loki and Thor.
Freyja's feather dress joins a long tradition of magical modes of transport, the most famous of which is probably Aladdin's magic carpet in One Thousand and One Nights (a.k.a. Arabian Nights). The ability to go from point A to point B very quickly may not seem so miraculous to modern folks, since we've got planes, trains, and automobiles, but the ancient Norse had to go on foot, on horseback, or on ships dependent on the weather for locomotion. Similarly, the Arabs went on camels, which explains the fascination that magical modes of transport must have held for them. These objects must have symbolized an incredible degree of ease and freedom.
Even after the creation of supersonic planes and bullet trains, however, we're still delighted by Harry Potter's floo powder and Nimbus 2000, or Star Trek's "Beam me up, Scotty." In our case, the fascination seems to be with the unusual or the instantaneous.