Swami Niranjan explains Sankalpa as a process of training the mind and to develop the will and to develop clarity of thought

With Sankalpa we can train the mind so that it becomes alive.

Due to our habit of being undisciplined we begin to weaken our will and Sankalpa is a way to strengthen it.

For an example Let us say that we are looking to change a habit, nature or obsession and rationally we do know how to do it but lack the motivation to do it. 

This lack of motivation creates a gap between what we want to do and what we actually do.

Sankalpa fulfills this gap and vaccum and provides us with motivation.

We donot need to start with a big Sankalpa we can start with small.

Swami Niranjan call a Sankalpa not only a thought, it is a power, it is a force.

Whatever we think with our mind we would project it in the environment around us.

If there is more power and force behind our thought our Sankalpa then we begin to attaract similar kind of circumstances around us and the stronger the force more strongly we would attract.

Sankalpa is just not a wish it is a conviction, it is trust and faith in oneself, in ones own strength and courage