First Timothy 2:5 declares, "For there is one God and one mediator between God and men, the man Christ Jesus." There is no one else that can mediate with God for us. If Jesus is the ONLY mediator, that indicates Mary and the saints cannot be mediators. They cannot mediate our prayer requests to God. Further, the Bible tells us that Jesus Christ Himself is interceding for us before the Father: "Therefore He is able to save completely those who come to God through Him, because He always lives to intercede for them" (Hebrews 7:25). With Jesus Himself interceding for us, why would we need Mary or the saints to intercede for us? Whom would God listen to more closely than His Son? Romans 8:26-27 describes the Holy Spirit interceding for us. With the 2nd and 3rd members of the Trinity already interceding for us before the Father in heaven, what possible need could there be to have Mary or the saints interceding for us?

[n]Extra Book included in Bible.[/b]
Roman Catholic need it to educate follower with "New" idea, they have to put it into the bible.

The Biggest FAILURE of a Jesus Follower
SMALL FAITH

Edit:
Hyperdulia - veneration due to the Blessed Virgin Mary (thus the addition of hyper because Mary is the most perfect model of all the saints)

Mary = Most Perfect Model of all the Saints??

1st. Jesus is the only Perfect Model.
2nd. Any human who closer to this Model would be PAUL
From Perspective of Theological Understanding, Missionary Achievement, Church Involvement.

Mary is just a blessed PERSON. Nothing more.
Catholic must Admit, most of them treated Mary as "demigod"

This is how Catholic goes into wrong path.

While :
"Therefore He is able to save completely those who come to God through Him, because He always lives to intercede for them" (Hebrews 7:25)

If Jesus told you HE can do it. ( meditate, intercede with GOD )

BUT You Replied :

Ok Lord Jesus. But i will also ask other to do it together

A Disgrace.

The point is NOT "Mary and the saints can most certainly intercede for us to God."
The Point is "When Jesus can do it for You", Why ask other?

God Is holy.
Trust and only Trust to God.
Worship and only Worship to God.
Have Faith to God Himself Alone.

Asian Religion usually practice this : Pray to many God is Better than Pray to 1 God

How i become a Christian?

Before Convert
I pray to Many God.

After Convert
Pray, worship, have faith to The Only God. Jesus

There is a temple in your heart.
Which is fit for God.
And only God himself stay there.

We shouldn't practice honouring the deceased church leader by given them superior spiritual status. So end up many people treat them as DEMIGOD..