Prayer to the saints is a Biblical teaching. It’s just not taught in one verse, as many would claim teachings need to be taught.
First let’s start by defining that to pray means to ask. Sure we can worship God while we pray and with our prayers. However, I am sure you would agree when we pray to God for help on an exam we are just asking for help, we aren’t worshiping Him with our exam. So when we pray to the saints or Mary we are simply asking them to pray with us to God.
The Bible commands us to pray for one another, here’s 2 of many… 1 Timothy 2:1 First of all, then, I urge that supplications, prayers, intercessions, and thanksgivings be made for all men, Matthew 5:44 But I say to you, Love your enemies and pray for those who persecute you,
Why does Jesus want us to pray for one another? Because scripture shows us that He will answer a weaker persons prayers based on the stronger person who is praying for them… Matthew 8:13 And to the centurion Jesus said, “Go; be it done for you as you have believed.” And the servant was healed at that very moment. Matthew 15:28 Then Jesus answered her, “O woman, great is your faith! Be it done for you as you desire.” And her daughter was healed instantly.
We also know that God will more readily answer the prayers of the righteous. James 5:16 Therefore confess your sins to one another, and pray for one another, that you may be healed. The prayer of a righteous man has great power in its effects.
Hebrews tells us that once we get to heaven we will be far more righteous than we are right now. Hebrews 12:22 But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering, 23 and to the assembly of the first-born who are enrolled in heaven, and to a judge who is God of all, and to the spirits of just men made perfect.