St. Louis meant exactly what he said, and that's how the Catholic Church sees it, because that's the way it actually is. She is our sweet, powerful, and unfailing intercessor.
And if you're a brother of Christ, she's your Mother, too. You have no idea how seriously God sees relationships. "Child of God" really means child of God, and "brother/sister of Christ" really means what it says. We have the same Heavenly Father, and the same Blessed Mother.
God is so much bigger than you Protestants portray Him. In fact, it stuns me as to how small you've made Him.
1 Tim. 2:5 For there is one God, and there is one mediator between God and men, the man Christ Jesus. John 14:6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me. Hos 13:2 And now they sin more and more, and have made them molten images of their silver, and idols according to their own understanding, all of it the work of the craftsmen: they say of them, Let the men that sacrifice kiss the calves.
Do you not recognize blasphemy when you read it?