1 Peter 2:17 - Peter teaches us to honor all men, love the brotherhood, fear God, honor the emperor. Don't those living with Christ in heaven deserve honor? Catholics believe they do, and honor them with special feast days, just as we honor those living by celebrating their birthdays.
If you are legitimately interested in understanding this I will expand upon it. If not, then no amount of supporting information will suffice.
Isaiah 42:8
That He does is unbiblical, and is just vain thoughts of a glory seeking, man made religion
Honoring someone is not the same as praying to them. That is what I have trouble with. Anyone praying to anyone other than God, through Jesus. Why can't you just honor those Saints or Mary IN your prayers, TO God and not pray to the Saints or Mary?