Lutheran pastor R. Daniel Carlson (LCMS) wrote on another public Facebook thread (his words in blue throughout):
Vain repetitions are what the pagans would do thinking that their non-existent pagan god could hear them if they said things enough times, or what a certain church domination does when they use a certain type of chain to pray to a certain woman whom they think can be prayed to instead of Jesus because they think she was perfect and can offer grace.
They also pray to Mary. Nothing in Scripture that says we should pray to the dead, that includes Mary and the saints who have gone before us. We pray to Jesus.
Nothing in Scripture says that we can or should pray to the Holy Spirit, and very few Scriptures refer to praying to Jesus (I can think of Stephen, as one).
As to human beings offering grace, that is entirely biblical. The Bible describes St. Paul acting as a “mini-mediator” of grace that originates, of course, from God. Paul distributes it to others:
2 Corinthians 4:15 (RSV) For it [his many sufferings: 4:8-12,17] is all for your sake, so that as grace extends to more and more people it may increase thanksgiving, to the glory of God.
Ephesians 3:2 assuming that you have heard of the stewardship of God’s grace that was given to me for you…
Ephesians 4:29 Let no evil talk come out of your mouths, but only such as is good for edifying, as fits the occasion, that it may impart grace to those who hear.
Beyond that, he is actually described as being a conduit of salvation as well:
Romans 11:13-14 Now I am speaking to you Gentiles. Inasmuch then as I am an apostle to the Gentiles, I magnify my ministry in order to make my fellow Jews jealous, and thus save some of them.
1 Corinthians 9:22 I have become all things to all men, that I might by all means save some.
2 Corinthians 1:6 If we are afflicted, it is for your comfort and salvation; . . .
2 Timothy 2:10 Therefore I endure everything for the sake of the elect, that they also may obtain salvation in Christ Jesus with its eternal glory.
That’s all we believe about Mary: she is being used mightily by God to help spread His grace and salvation, just as the Apostle Paul did.
We pray to her, to ask her to intercede with her Son and God the Father, because “The prayer of a righteous man has great power in its effects.” (James 5:16). The exceptionally holy, righteous person has a lot more power to achieve a petition with God, so we utilize that power in our own petitions and intercessions.
The saints in heaven are “dead” only from our perspective: having departed this earthly life. But they are more alive than we are, and actively, lovingly aware of what goes on, on the earth. They’re not merely floating on clouds and playing harps for all eternity.
No biggie at all; completely, explicitly biblical on all counts.
As for the Rosary being vain repetition, I’ve written about that charge:
Mary, the mother of our Lord, would slap you silly if she knew that you prayed to her instead of through her Son. Nothing in Scripture suggests or implies that she, or the rest of the saints who have gone before, can hear you — but only Christ who stands before the Father. And we have only one Father, and one Lord and Savior Jesus Christ, both from whom the Spirit proceeds.
What’s wrong with asking Christ to intercede for us — He who is our mediator as we read in Scripture — He who is our High Priest and the One who stands before the Father for our sakes? Is this insufficient?
Nothing whatsoever, and yes, of course it is sufficient. This is simply Protestant either/or reasoning: if we ask anyone else to pray for us, somehow we must be running down God or prayer to God as insufficient and/or inferior.
None of that follows. The Bible teaches that we pray for each other, and ask others to pray for us. I already gave the scriptural rationale for praying to Mary (or, more accurately, asking her to intercede for us): it’s based on righteous persons’ prayers having more power. James gave the example of Elijah: he prayed and it stopped raining for three-and-a-half years, and then it started again when he prayed for that.
So in James 5 the model of Elijah is used to illustrate a principle: holy people can pray for others, and their prayers have relatively more power. It doesn’t just say, “pray to God and never ask anyone else to pray for you.” Rather, the text says:
James 5:14 Is any among you sick? Let him call for the elders of the church, and let them pray over him . . .
So we apply that to the saints in heaven, because they have far more power than anyone on earth: having been perfected in glory. We know that they pray for us (even your Lutheran Confessions concede that). We know that they are acutely interested in the affairs of earth, from Hebrews 12:1 (“we are surrounded by so great a cloud of witnesses”): which commentators have explained as like a stadium of spectators watching us. Therefore, we ask them to pray for us, because we know that their prayers (like Elijah’s) have more power than ours.