@Terese idolatry is considered to be a sinful practice in Abrahamic faiths, because
worship should be rightly owed only to someone greater than ourselves and not to someone or something intrinsically equal to us in nature; even less something which is actually
inferior to us.
As it is written in the Book of Wisdom (13:17-19; 15:16-17), from the Catholic/Orthodox Old Testament:
"When he prays about possessions and his marriage and children,
he is not ashamed to address a lifeless thing.
For health he appeals to a thing that is weak;
for life he prays to a thing that is dead;
for aid he entreats a thing that is utterly inexperienced;
for a prosperous journey, a thing that cannot take a step;
for money-making and work and success with his hands
he asks strength of a thing whose hands have no strength.
For they thought that all their heathen idols were gods,
though these have neither the use of their eyes to see with,
nor nostrils with which to draw breath,
nor ears with which to hear,
nor fingers to feel with,
and their feet are of no use for walking.
For a human being made them,
and one whose spirit is borrowed formed them;
for none can form gods that are like themselves.
People are mortal, and what they make with lawless hands is lifeless;
for they are better than the objects they worship,
since they have life, but the idols never had. "
When human beings started personifying objects constructed out of wood, stone clay or precious metal with divine identities and powers, regarding them to be worthy of worship, they began a distressing trend -
not in malice but accidentally - that would end in the worship of other human beings, their equals by nature now exalted to divine status (i.e. god-kings and priest-kings like the Roman emperors, Chinese emperors etc.).
The same
Book of Wisdom explains how this, in the view of its sacred author, developed over time:
"The invention of them [idols] was the corruption of life;
for they did not exist from the beginning,
nor will they last for ever.
For through human vanity they entered the world,
and therefore their speedy end has been planned.
For a father, consumed with grief at an untimely bereavement,
made an image of his child, who had been suddenly taken from him;
he now honoured as a god what was once a dead human being,
and handed on to his dependants secret rites and initiations.
Then the ungodly custom, grown strong with time, was kept as a law,
and at the command of monarchs carved images were worshipped.
When people could not honour monarchs in their presence, since they lived at a distance,
they imagined their appearance far away,
and made a visible image of the king whom they honoured,
so that by their zeal they might flatter the absent one as though present.
Then the ambition of the artisan impelled
even those who did not know the king to intensify their worship.
For he, perhaps wishing to please his ruler,
skilfully forced the likeness to take more beautiful form,
and the multitude, attracted by the charm of his work,
now regarded as an object of worship the one whom shortly before,
they had honoured as a human being.
And this became a hidden trap for humankind,
because people, in bondage to misfortune or to royal authority,
bestowed on objects of stone or wood the name that ought not to be shared."
Human beings, in the Abrahamic mindset, are of far greater worth than any object we can fashion with our own hands. Moreover we were all created equal in the image of God. For this reason we shouldn't worship anything lesser than ourselves - such as lifeless works of art - or which God had intended to share equal status with us, such as our fellow human beings.
All that said, the Catholic tradition has always encouraged the use by believers of sacred statues/icons/images representing the Lord Jesus or the Mother of God, or the saints. From an exterior vantage point, our devotional practices don't look a whole lot dissimilar from what Hindus do in relation to Vishnu, or Shakti or Krishna etc. We are the least doctrinaire among Abrahamic religions about that sort of thing (i.e. we have no problem about depicting God in images), although we do not regard praying before a statue - using it as an aid to visualize the entity or person we are actually praying to, or indeed worshiping in the case of Jesus - to be "
idolatrous" in any way, because we aren't actually worshiping the wood or stone but the Divine Person it represents (in the case of the Blessed Virgin or a saint, we are merely praying to them/honouring them but never offering worship since they are human beings like us, however glorified and beatified).