Question: "Is worship of saints / Mary biblical?"
Answer: The Bible is absolutely clear that we are to worship God alone. The only instances of anyone other than God receiving worship in the Bible are false gods, which are Satan and his demons. All followers of the Lord God refuse worship. Peter and the apostles refused to be worshipped (Acts 10:25-26; 14:13-14). The holy angels refuse to be worshipped (Revelation 19:10; 22:9). The response is always the same, "Worship God!"
Roman Catholics attempt to "bypass" these clear Scriptural principles by claiming they do not “worship” Mary or saints, but rather that they only "venerate" Mary and the saints. Using a different word does not change the essence of what is being done. A definition of "venerate" is "to regard with respect or reverence." Nowhere in the Bible are we told to revere anyone but God alone. There is nothing wrong with respecting those faithful Christians who have gone before us (see Hebrews chapter 11). There is nothing wrong with honoring Mary as the earthly mother of Jesus. The Bible describes Mary as "highly favored" by God (Luke 1:28). At the same time, there is no instruction in the Bible to revere those whom have gone to Heaven. We are to follow their example, yes, but worship, revere, or venerate, no!
When forced to admit that they do, in fact, worship Mary, Catholics will claim that they worship God through her, by praising the wonderful creation that God has made. Mary, in their minds, is the most beautiful and wonderful creation of God, and by praising her, they are praising her Creator. For Catholics, this is analogous to directing praise to an artist by praising his sculpture or painting. The problem with this is that God explicitly commands against worshipping Him through created things. We are not to bow down and worship anything in the form of heaven above or earth below (Exodus 20:4-5). Romans 1:25 could not be more clear, "They exchanged the truth of God for a lie, and worshiped and served created things rather than the Creator — who is forever praised. Amen." Yes, God has created wonderful and amazing things. Yes, Mary was a godly woman who is worthy of our respect. No, we absolutely are not to worship God "vicariously" by praising things (or people) He has created. Doing so is blatant idolatry.
The major way Catholics "venerate" Mary and the saints is by praying to them. As the following article demonstrates, prayer to anyone other than God alone is anti-Biblical – praying to saints and Mary. Whether Mary and/or the saints are prayed to, or whether they are petitioned for their prayers – neither practice is Biblical. Prayer is an act of worship. When we pray to God, we are admitting that we need His help. Directing our prayers to anyone other than God is robbing God of the glory that is His alone.
Another way Catholics "venerate" Mary and the saints is by creating statues and images of them. Many Catholics use images of Mary and/or the saints as "good luck charms." Any cursory reading of the Bible will reveal this practice as blatant idolatry (Exodus 20:4-6; 1 Corinthians 12:1-2; 1 John 5:21). Rubbing rosary beads is idolatry. Lighting candles before a statue or portrayal of a saint is idolatry. Burying a Joseph statue in hopes of selling your home (and countless other Catholic practices) is idolatry.
The terminology is not the issue. Whether the practice is described as "worship" or "veneration," or any other term, the problem is the same. Any time we ascribe something that belongs to God, to someone else, it is idolatry. The Bible nowhere instructs us to revere, pray to, rely on, or "idolize" anyone other than God. We are to worship God alone. Glory, praise, and honor belong to God alone. Only God is worthy to "...receive glory and honor and power..." (Revelation 4:11). God alone is worthy to receive our worship, adoration, and praise (Nehemiah 9:6; Revelation 15:4).