The ability of humans (and some animals) to close our hand or hands around an object means we can exert greater control over our environment. We can pick up and eat food. We can raise objects in a hand, carry objects, throw them, etc.
hand
Pincer?
the Flexorum digitorum
In poker, a hand with 3 of a kind has the advantage over a hand with 2 pairs.
The human hand is made up of the palm, fingers, and thumb collectively. It is an essential tool we utilize for grasping, manipulating objects, and performing various tasks.
The influence of photographs is the better grasping of the subject at hand; a picture is worth a thousand words.
Farmers harvest it by grasping it in one hand then cutting it at the base with a sickle, then when they have done this to a whole field of it they collect it
The Brandt Andrew Maneuver is a method of expressing the placenta after child birth by grasping the umbilical cord with one hand and placing the other hand on the abdomen.
The cast of Hot Hand Advantage - 2006 includes: Brett Granstaff as himself
it does most of the work for you
The muscle action you are referring to is called adduction. This movement brings the thumb towards the palm of the hand. Adduction is an important function that allows for gripping and grasping objects with the hand.
Without the thumb, the fingers and hand can not make prehensile movements. That is what grasping needs...the thumb.