Every thing about the Orthodox Church that is not explicitly in the Scriptures has an ancient pedigree.
For example, no Biblical verse unmistakably says, “Baptize babies.” Neither does a Biblical verse say, “Don’t baptize babies.” Thus we have to use our noggin. Of course, plausible arguments can be made either way. I like to look to history to cut the Gordian knot, since exegetical arguments are endless. We have pre-Constantinian writers mentioning the baptism of babies, and none of them that I’m aware of say, “Don’t baptize babies!” or “We recently started baptizing babies.” On the contrary, it is presented as something correct and of long use. If infant baptism was an innovation, where was the controversy? Where was the debate over its merits?
The same goes for icons, infant communion, and all the rest. Whenever a controversy did arise over something, it was usually someone in a position of authority saying, “I think the Church should STOP doing X.” For example, Arius saying that the Church should stop regarding Jesus as God, or Nestorius saying that the Church should stop describing Mary as the Theotokos, or the Emperor (I forget his name) saying that the Church should stop venerating icons, or Barlaam saying that the Church should stop believing in God’s uncreated Energies, etc. In other words, the heretics are always innovators. They want to change what has always been done.
The question of the veneration of Mary and all the saints is an interesting one. It is vital to remember that the early Church kept most of its liturgy secret from non-members. Even to this day there is a part of the Sunday liturgy that proclaims, “All catechumens, depart. Depart catechumens. All that are catechumens depart. Let no catechumen remain. Let us, the faithful, again and again in peace pray unto the Lord.” This happens rather near the beginning of the liturgy, after only A) some prayers and psalms, B) the Scripture readings, and C) a homily. In other words, the “open to all” part of the liturgy contains only stuff that could have been read by anybody without even attending a liturgy. The rest of the liturgy was for baptized members only. (This, BTW, helps explain the paucity of surviving liturgical materials from the early Church. That stuff was secret! It was for members only.)
Whenever I go to liturgy, I am surrounded by icons of Christ, Mary, and the saints. An icon is not a picture of someone who is absent. It is a divine sign of that person’s presence. We believe that when we perform the liturgy, we are joining the Liturgy in Heaven. We are literally worshipping alongside the Virgin Mary, and the Apostle Peter, and the Apostle Paul, and all the saints and all the angels and all those in Heaven. We are in their presence no less surely and literally than we are in the presence of those physically standing next to us in the church–such as my neighbor Frank, the old Slavic guy (Robert), the guy who teaches ballet (Misha), the new member (Ian), the priest’s wife (Natalia), etc. When I see Frank, Robert, Misha, and all the rest, do I ignore them? No! I bow to them. They bow to me. We bow to the priest. The priest bows to us. Every single person acknowledges every other single person. Why? Because each of us is the Image of God. How could we ignore God’s Image?
For the same reason that we all bow to each other, we bow to the icons. The Apostle Peter is really there, worshipping along with us. It would be the height of insanity to ignore the Apostle in our midst! And if he weren’t there, then I just would not be interested. I’ll either go to Church with all the Apostles and all the rest of the heroes of the Bible, or I won’t go at all.
We talk to Mary and to all the angels and saints during our liturgy. How could we not? They are present with us! After all, the Psalmist even talks to inanimate nature. If the Psalmist can talk to and make requests of hills, waters, etc., then how much more so is it good to talk to and make requests of Mary, Peter, Paul, John, etc.
Further, we praise those in Heaven because they have been thoroughly deified. They utterly participate in the Divine Nature (as Peter wrote). They are utterly sinless. They are now perfect Images of Christ. Or, as St. Irenaeus wrote: “God became man so that man might become God.” Everything God is by nature, they are by grace. One day it will be so with us.
The experience of the saints in the Church is unavoidable. The only alternative would be to pretend that Mary, Paul, John, etc. are not there:
“Look! There’s Mary!”
“Shhhhhhh! Pretend she isn’t here.”
“Huh?”
We aren’t in Church to pretend, but to rejoice, and to rejoice in God with all creation.