Well, Dani, let me first say that Roman Catholicism with their teaching of Inclusivism and Eastern Orthodoxy with their hopeful universalism, do have more in common with universalists, then universalists have with exclusive evangelical Protestantism.
If you live in the US, you can actually have an adult reference, public library librarian research questions life this - for free. And you can also ask a Roman Catholic priest and Eastern Orthodox priest, for their responses. If you do that, you will find a better understanding of what they do and why they do it. A baptist minister with a PHD in theology from a Catholic university, was a professor of my at the College of DuPage. He said that Congregational, Pentecostal worship and liturgical worship were all present around the time of Christ or shortly thereafter.
Regardless of the Protestant viewpoints propagated, RC and EO clergy will say they have saints pray for them, they venerate them, etc., but it’s forbidden to worship them, as worship is referred to God alone.
. Look at the section Origin but it is vague on specific dates.
Bones of saints are called relics. Go to the Wiki Christianity section on relics
People believe in things like relics, Pentecostal healing, sacred sites, Native American ceremonies, etc., because people have experienced healing by doing so. Now we can argue that it’s placebo effect, unknown powers of the mind, etc. But if something didn’t work - regardless if it’s a statistical correlation, they wouldn’t follow it.
So back to my summary. An EO and RC priest can explain why they do what they do and clear up misconceptions. A public reference librarian can research the date stuff and give sources. But our job is to better understand it - not necessarily agree with it.