The answer to this question has many levels. Modern people have many varying beliefs and while respecting this, I offer the following perspectives…
There are three main drivers for blessing a carving; 1) Historical, 2) Cleansing and Transforming, 3) Other Various Beliefs.
1 - Historically:
Within Māori culture, it is customary to bless a carving. This relates to any carving whether it is bone, stone, or wood. This is a vast subject that requires extensive background information, however I will briefly summarise some of my small understandings of this topic.
The first concepts to understand are Tapu and Noa.
Tapu: The meaning of Tapu is to be sacred, prohibited, restricted, set apart, forbidden, under atua protection. (Atua meaning supernatural entities; gods, demons or deitys).
Something or someone that is Tapu is put into the sphere of the sacred. It is untouchable, no longer to be put to common use. The violation of tapu would result in retribution, sometimes including the death of the violator and others involved directly or indirectly. Appropriate karakia (prayers) and ceremonies could mitigate these effects. Making an object tapu was achieved through rangatira (Chiefs) or tohunga (expert/healer) acting as channels for the atua in applying the tapu.
Tohunga Whakairo (Master Carvers) were traditionally the holders and teachers of knowledge about the spiritual realms. Thus, all that they created was initially classed as Tapu or scared.
Noa: When tapu is removed, things become noa, the process being called whakanoa. This means that the object that was Tapu is now free from restrictions. It is now able to be put to common use.
In summary, when something is Tapu it has restrictions, when it is Noa, it is free from restrictions. Blessing a carving frees it from being Tapu and is therefore free from restrictions.
2 - Cleansing and transforming:
The energy of the artist imbues the carving due to their concentration and intimacy with their creation. Because of this, it is possible for their general temperaments, moods and various thought processes to mix with the carving.
Sometimes this may be a good thing. For example, if the artist is thinking positive or virtuous thoughts. Indeed, some carvers with esoteric understandings will consciously imbue their Taonga with concentrations of love, mantra (mind protection), prayers or other incantations while making them.
However, on the other side, there may be negativities arising through the mind of the artist while making them. So, if the artisan is not able to control their mind perfectly, then it is possible for non-virtuous minds to arise and negatively effect the carving. (For example, if the artist if feeling non-peaceful, grumpy, anxious, or has strong un-controlled desire etc).
Our mind is very powerful and whatever we think affects others. For example, when you walk into a room it is possible for many people to sense the atmosphere of the environment that they are entering. There are many examples of how people can pick up on the thoughts and energies of others (even over long distances). Therefore we can understand through this how the mind of the carver will impact on their creation.
For this reason, many people like to have their carving blessed. This blessing, if done correctly, will purify the carving of any negativity that have been inadvertently placed into it during the process of its creation. Further to this, one who is qualified, may go a step further and invite powerful blessings of various holy beings to raise the vibration of the carving and thereby transform it into a true treasure…Such a Taonga will subtly bless the minds of all those who encounter it.
3 - Other Various Beliefs:
There are many other personal beliefs regarding why a carving should be blessed. For example, some people believe that various spirits come to inhabit a carving upon its completion. There are over 80 thousand classes of spirit, so it is certainly not out of the realm of possibility that a spirit would like to inhabit or “impute” itself upon such attractive forms. A blessing in this case would cleanse the carving of any malevolent manifestations.
I have had many unexplained experiences relating to these matters. Just the other day a carver friend was telling me about a carving he did which had an adverse effect on someone. Every time they wore it, their heart starting racing very fast. They told him about it and he advised them on how to go about blessing it. They did so and then instantly the problem disappeared.
There are many people in the world who understand the existence of a spiritual dimension. That which exists beyond our ordinary understanding or sense awareness. Some have discovered such a reality and are able to utilise its structures and universal laws. As such they can tap into reservoirs of immense strength and power.
This reality continues to be explored today and no matter what your personal beliefs, I think everyone would agree that if a blessing increases our love and compassion for others and deepens our inner peace, then it is a good thing.
In summary, a blessing will pacify negativity and increase goodness.