In Psalm 103 we pray, “Bless the Lord, O you his angels, you mighty ones who do his word, hearkening to the voice of his word! Bless the Lord, all his hosts, his ministers that do his will!” (Ps. 103:20-21). And in Psalm 148 we pray, “Praise the Lord! Praise the Lord from the heavens, praise him in the heights! Praise him, all his angels, praise him, all his host!” (Ps. 148:1-2)
Not only do those in heaven pray with us, they also pray for us. In Revelation, John sees that “the twenty-four elders [the leaders of the people of God in heaven] fell down before the Lamb, each holding a harp, and with golden bowls full of incense, which are the prayers of the saints” (Rev. 5:8). Thus the saints in heaven offer to God the prayers of the saints on earth.
Angels do the same thing: “An] angel came and stood at the altar [in heaven] with a golden censer; and he was given much incense to mingle with the prayers of all the saints upon the golden altar before the throne; and the smoke of the incense rose with the prayers of the saints from the hand of the angel before God” (Rev. 8:3-4).
Jesus himself warned us not to mess with small children because their guardian angels have guaranteed intercessory access to the Father: “See that you do not despise one of these little ones; for I tell you that in heaven their angels always see the face of my Father who is in heaven.” (Matt. 18:10).
Tobit 12:12 So when you and Sarah prayed, it was I who brought the record of your prayer into God’s glorious presence, and likewise when you used to bury the dead. (said the Angel Raphael)
And in Joshua 5:14, “Neither,” he replied, “but as commander of the army of the LORD I have now come.” Then Joshua fell facedown to the ground in reverence, and asked him, “What message does my Lord have for his servant?”
If bowing to others out of reverence is a sin, how do protestants explain: Joshua 5:14, Ruth 2:8-10, 2 Kings 4:37, Genesis 19:1. 1 Samuel 24:8, 1 Kings 1:16, 25, Genesis 33:3, Genesis 27:29?
And if asking others to intercede for us is a sin, why does S.t Paul ask others to pray for him in his Epistles? why doesn’t he just pray directly to God?
A great book I would recommend on this topic is, "Any Friend of God is A Friend of Mine, by Patrick Madrid.