I'm glad you asked that. Intercession comes from Scripture.
The apostle Paul frequently asked other fellow believers in Jesus to pray for him.
Col 4:3
At the same time, pray for us, too, that God may open a door to us for the word, to speak of the mystery of Christ, for which I am in prison.
Rom 15:30
... join me in the struggle by your prayers to God on my behalf,
James asks presbyter believers to pray over other believers.
Jam 5:14
Is anyone among you sick? He should summon the presbyters of the church, and they should pray over him and anoint (him) with oil in the name of the Lord
"you are no longer strangers and sojourners, but you are fellow citizens with the saints and members of the household of God, built upon the foundations of the apostles and prophets, Christ Jesus himself being the cornerstone." (Eph 2:19-20
Catholic Christians believe that as we can ask a fellow Christian -a saint- to pray for us, we should be able to ask prayers from the saints already united to the Lord in heaven. If the prayers of certain Christians here on earth seem to possess special power because of their great faith witness or holiness, how much more powerful and effective might not the prayers of those of the communion of saints in heaven who are fully united to God.
There are many other references to saints, praying for each other, and offering prayers to God through those already in Heaven. I would be happy to cite them.
God bless.
Prayer is worship. Praying to Mary is worship of Mary. I pray to God the Father in Jesus' name, acknowledging the great debt that I owe Him. So are you saying that Mary can accomplish what the Lord cannot?
When you read of the first miracle performed by the Lord in John, how do you yourself, understand it? Thanks. God bless you as well.