Imagine praying to a skeleton named St. Death when Jesus tells us in Matt. 6:6 & 9 to pray to our Father who art in heaven and to ask it all in Jesus' name (John 14:13).  This may not be a graven image, but it still amounts to idolatry since their is only "one mediator between God and men, the man Jesus Christ" according to 1 Timothy 2:5.
 
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