electric field

Electric field is defined as the force on a positive test charge placed there.

To know the existance of a field, one needs to measure the force on a charge.

If you place a charge and say that there is an electric field around it. How will you find the strength of this field?

You will measure the force on a charge and then divide the force by that charge to find the field at that location in space. So to measure the field the force needs to be found.

Look at it the other way. You know the field at a point. Now you know the force that any charge placed at that point will experience!