What is the meaning in the Buddha walking seven steps?
According to Mahāpadā­na­sutta, when he was born he stood firm on both feet, then with his face to the north took seven strides while a white canopy was held over him. There is no mention of a shower at every step though.

According to Mahāpadā­na­sutta commentary, standing firm on both feet is a portend for achieving the four iddhipada (Intention, Effort, Consciousness, Investigation). Facing north is a sign that he'll rise above others, the seven steps he walked is a portend that he'll achieve the seven factors of enlightenment (satta bojjhaṅgā) and finally the white canopy held over his head is a symbol that he'll achieve nirvana.