The Bible says there is only One to whom you must direct your prayer, and He is God.
Mary, the mother of Jesus had an important role to play in God’s plan of salvation. Her role was to bring Jesus into the world. The Gospel writer Luke has recorded for us what the angel Gabriel told Mary about her role: “Do not be afraid, Mary; you have found favor with God. You will conceive and give birth to a son, and you are to call him Jesus. He will be great and will be called the Son of the Most High. The Lord God will give him the throne of his father David, and he will reign over Jacob’s descendants forever; his kingdom will never end.” (Luke 1:31-33)
Mary was a good and loving mother to Jesus from the time He was born to after He was crucified and raised from the dead. In Acts 1:14 we read “They all joined together constantly in prayer, along with the women and Mary the mother of Jesus, and with his brothers.” Mary, like all the others prayed to God. And on the day of Pentecost Mary was there with the other disciples of Jesus when, “Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.” (Acts 2:2-4)
Mary was a loving mother and faithful disciple of Jesus. Mary is not God. We should not pray to her and she never asked us to do so. Jesus, on the other hand has asked us to pray to Him: “And I will do whatever you ask in my name, so that the Father may be glorified in the Son. You may ask me for anything in my name, and I will do it.’ (John 14:13-14)
It is Jesus and not Mary who intercedes for us: “Therefore he (Jesus) is able to save completely those who come to God through him, because he always lives to intercede for them.” (Hebrews 7:25)
It is very clearly stated in 1 Timothy 2: 5-6 that only Jesus can carry our prayers to God: “ For there is one God and one mediator between God and mankind, the man Christ Jesus, who gave himself as a ransom for all people.”
It is Jesus who died for our sins and it is only through Him we can have access to God.
In the commandment God gave He says: “You shall not make for yourself an idol in the form of anything in heaven above or on the earth beneath or in the waters below. You shall not bow down to them or worship them; for I, the LORD your God, am a jealous God…” (Exodus 20:4-5). ‘Jealous’ here means God will not have us give to another what rightly belongs to Him. We worship God and pray to Him and no one else. So, is praying to anyone, other than God a sin? Yes it is.