Question

how does fundamental duties bring a holistic development in the country ?

Answer 1

Start with the proposition that consensus is easier to establish for general principles than for specific directives. Who, for example, would disagree with the statement: "Everyone should be treated with dignity"? Compare the foregoing non-controversial statement with the more specific: "By scolding John in front of his classmates for playing video games in class, the teacher failed to respect John's dignity." We can easily imagine disagreements as to whether the teacher's scolding was proportionate to the misbehavior. Or, take another example: "Persons who have not paid for health insurance are not treated with requisite dignity when they are denied admission to a top-tier hospital for expensive treatment." No doubt, disagreements will arise as to why the person did not pay insurance. Was he /she able to afford the insurance? What level of care will (should) he/she receive notwithstanding the non-payment? 
With the foregoing in mind, if a society (country? neighborhood?) can generate consensus around basic principles, particularly in civic discourse, then perhaps we can move incrementally to consensus as to less general statements. Of course, societies are dynamic and the grounds for consensus shift even as consensus emerges and therein lies the vexation and challenge.