Why is field theory necessary?

Hint:Field theory usually refers to a description of a field's dynamics, i.e., how a field changes over time or in relation to other independent physical variables on which the field depends. This is usually accomplished by constructing a Lagrangian or Hamiltonian of the field and treating it as a classical or quantum mechanical system with an infinite number of degrees of freedom. Classical and quantum field theories are the two types of field theories that result.

Complete step by step solution:
Field theory is significant for a variety of reasons:
It's simple to comprehend and offers us a sense of how particles will react when placed at different points in the field.
When a unit positive charge is placed at any location in the system, magnetic and electric field theory can be utilized to calculate the magnetic/electric force.
It also aids us in comprehending the effects of a specific force (represented by the field) when applied in various magnitudes and positions, as well as in many positions at the same time.
When dealing with charges in motion, the physical significance of field theories such as Electric field theories becomes even more essential. When a charged particle moves, it transmits its motion/acceleration to neighboring charged particles in the form of a disturbance that travels at the speed of light. The electromagnetic wave is a disturbance caused by the superposition of a time-varying electric field and a magnetic field of an accelerated charged particle (e.m. wave)

Note:A field theory is a description of a field's attributes and knowledge. Field theories are available in a variety of flavors.
Classical field theory
Statistical field theory
Quantum field theory
Thermal field theory
Information field theory