Thomas Aquinas,
Summa Theologiae — Question 83 - OF PRAYER…
“ I answer that, Prayer is offered to a person in two ways: first, as to be fulfilled by him, secondly, as to be obtained through him. In the first way we offer prayer to God alone, since all our prayers ought to be directed to the acquisition of grace and glory, which God alone gives, according to Ps. 83:12, "The Lord will give grace and glory." But in the second way we pray to the saints, whether angels or men, not that God may through them know our petitions, but that our prayers may be effective through their prayers and merits. ”
