As a counterpart to Rory showing her grandmother the potting shed, Rachel shows Lorelai Luke’s apartment when she comes over. Like the potting shed, it was never designed to be used as living quarters (it was Luke’s father’s office for the hardware store), and is impractical for a couple to live in together. This shows an affinity between Luke and Lorelai – both will settle for a cheap, uncomfortable living space if they need to save money; both are willing to wait in order to reach long-term goals. (And how they wait!)
Lorelai is amused to discover that the supposedly curtain-hating Luke picked out some floral curtains for his own apartment. She is clearly very intrigued to see where Luke lives.