Question:Can you please help me explain to a Catholic why it is not right to call Mary ''our heavenly mother'' ?
The problem is that Mary is not our mother in any sense of the word. God is our Father because He created man. God is in heaven so it is proper to talk about our heavenly Father versus our earthly father (Matthew 6:14). The implication of "heavenly Father" is that we are speaking of deity; something that Mary is not.
When people die, the Bible teaches that they go to hades until the day of judgment. Even Abraham was seen to be in this realm (Luke 16:23). Jesus, upon his death and before his resurrection, was in this realm (Acts 2:31). Therefore, Mary is not yet in heaven as she has not yet been resurrected. Roman Catholics avoid this problem by claiming that Mary was bodily assumed into heaven; Yet it has one major flaw -- the God never said this happened. It doesn't appear in the Bible -- it is a myth, a man-made fable and not the truth.
Thus, the phrase fails to be biblical on two accounts. "For the time will come when they will not endure sound doctrine, but according to their own desires, because they have itching ears, they will heap up for themselves teachers; and they will turn their ears away from the truth, and be turned aside to fables" (II Timothy 4:3-4).