Symbolically Devout
Although she's perhaps best know for a fantastic, odd, and sexualized poem called "The Goblin Market," the bulk of Christina Rossetti's work reflected her life of Christian devotion. Much like in "A Birthday," she wasn't just putting her faith nakedly out there. Instead, she relied heavily on Christian symbols to communicate her faith. You can check out examples of this approach in poems like "A Better Resurrection" or "Up-Hill".