Something I don't understand: how can Catholics pray for intercession of someone who is not Jesus Christ, the only intercessor (as per Romans 8)? If you'd rather not get into it here, I understand, but your statement just stirred up that thought in my mind.
18 Praying always with all prayer and supplication in the Spirit, and watching thereunto with all perseverance and supplication for all saints; 19 And for me, that utterance may be given unto me, that I may open my mouth boldly, to make known the mystery of the gospel,There are other reasons, but that's the first New Testament reference I thought of.