Which Article of the Indian Constitution makes it clear that Directive Principles of State Policy are fundamental in the governance of the country and it shall be the duty of the state to apply these principles in making laws?

Article 37 of the Indian Constitution explicitly states that the provisions contained in Part IV (Directive Principles of State Policy) shall not be enforceable by any court, but the principles therein laid down are nevertheless fundamental in the governance of the country and it shall be the duty of the State to apply these principles in making laws.
Article 40: Organisation of village panchayats.

Article 44: Uniform civil code for the citizens.

Article 46: Promotion of educational and economic interests of Scheduled Castes, Scheduled Tribes and other weaker sections.