It must be very difficult for Protestants who convert to Catholicism to approach the idea of “praying to Mary and the saints”. This is an entirely alien concept and, as such, must be somewhat frightening. If you are sincerely wondering what the “communion of saints” is all about in Catholicism, you will first need to suspend disbelief for a moment. I have found it quite perplexing, by the way, that some Protestant churches pray the “Apostles Creed” (which was composed by Catholics) and never seem to trip over the lines “I believe in the Holy Spirit; the holy catholic Church; the communion of saints”.
“Many people who do not share the Catholic Christian faith have difficulty with the appearance that Catholics pray to Saints and Mary, as one prays to God. This “praying to” appears to them to indicate a worship of the Saint or Mary what is due to God alone. However,
earliest Christianity has always defined prayer as conversation, as in conversation with God. Conversation as any other act of communication requires a sign of the direction of the communication: one talks to someone, communicates with someone, prays to someone, etc.
Hence, praying to God, a Saint, the Virgin Mary indicates simply the direction of prayer communication. It is more a matter of grammar and understanding communication than acknowledging the worship of the receiver.”
thesacredheart.com/inte.htm
This article answers your question more fully:
stmonica.cc/papers/interces.htm
Early Church Fathers seem to carry a lot of weight with Protestants, so here are some quotes:
St. Cyril of Jerusalem in his
Catechetical Lectures, which were composed around the year 350, wrote the following. "Then we make mention also of those who have already fallen asleep; first, the patriarchs, prophets, Apostles, and martyrs, that through their prayers and supplication God would receive our petition."5
St. Augustine preached twice weekly from the time of his ordination in 391 until his death in 430. He had this to say on our subject. "Prayer, however, is offered for other dead who are remembered. For it is wrong to pray for a martyr, to whose prayers we ought ourselves be commended."6 In his work,
Against Faustus, written around the year 400, he writes: "A Christian people celebrates together in religious solemnity the memorials of the martyrs, both to encourage their being imitated and so that it can share in their merits and be aided by their prayers."7