Why is the god Ganesha decorated ceremoniously and worshiped lovingly for a few days, and then immersed in water? – either thrown into the sea or a river or a lake.
But there is a beautiful concept behind this immersion
The real secret of worship is in making an idol and then letting it disappear... giving a shape and form to the idol and then letting it vanish into the formless. It is all symbolic – the act of making an idol of the goddess Kali, worshiping it, and then immersing it in water.
But we don’t worship in the right way: we have made the idol, decorated it beautifully and looked after it, so then we are reluctant to let it go by immersing it.

If we had really worshiped, worshiped in the deepest sense, then the idol would have disappeared inside us, crystallized inside us, long before we let it disappear into the water.
If the real worship had happened then there would have been no need to immerse the idol at all, it might have remained where it was but the heart of the worshiper would have been immersed into existence, into the divine. Then, if we had gone to immerse the idol it would have
been like throwing away a used cartridge; it would have done its work.
But the idol which we immerse is a loaded cartridge – unused and still alive. We have just loaded the cartridge and we have to immediately throw it away, so naturally we are unhappy about it.
In earlier times, during the twenty one days of worship, the cartridge was fired, it had served its purpose during that time the immersion or disappearance of the idol had happened.
Worship is immersion

If you stop at the idol you do not know what worship is. Whoever continues on to worship has recognized the idol, has known the root of worship and the real purpose of the idol.