Christina Rossetti is known for her religious convictions. In fact, when she wasn't writing poetry, she was putting together non-fiction books with titles like Called to Be Saints. It should come as no great shock, then, to learn that there are a ton, a slew, a plethora of Christian symbols and imagery going on in this poem—particularly in stanza 2. Rather than talk about them each one at a time, we thought we'd just put them all right here for your convenience. No need to thank us—we know you're busy people.
Lines 3-4: The apple is a biblically significant fruit. It's typically associated with the forbidden fruit that hung from the Tree of Knowledge of Good and Evil, and which Eve was tempted by Satan into trying. In these lines, though, the tree in question is heavy with ripe, "thickset" apples. The image here is one of plentitude and satisfaction.
Lines 9-10: A "dais" is a special platform, something you'd rest a throne or an altar on. This one seems to be super-special, since the speaker calls for it to be decorated with fur, silk, down (comfy bird feathers), and purple (a color that symbolizes royalty). This is a place for a Very Important Person, and God naturally fits that bill.
Lines 11-12: We get more religiously resonant decorations in these lines. Doves symbolize both peace and God's mercy (in ending the great flood). Pomegranates were decorations that King Solomon had carved into the pillars of his temple, and they are often associated with Jesus's suffering and rebirth. Even peacocks have religious significance here. They were thought to have immortal flesh, so they came to symbolize the everlasting life promised by God, as well as His all-seeing presence in our lives (as shown by many "eyes" that decorate a peacock's tail).
Lines 13-14: In these lines, grapes (and wine) symbolize the blood of Christ and commemorate His sacrifice for humanity. The fleur-de-lys is also a symbol, representing the lily flower— which, in turn, stands for purity and the Virgin Mary.