A 5-judge Constitutional Bench held as follows regarding when the need of interpreting a statute arises.

The interpretative function of the Court is to discover the true legislative intent. It is trite that in interpreting a statute the Court must, if the words are clear, plain, unambiguous and reasonably susceptible to only one meaning, give to the words that meaning, irrespective of the consequences. Those words must be expounded in their natural and ordinary sense. When a language is plain and unambiguous and admits of only one meaning no question of construction of statute arises, for the Act speaks for itself. Courts are not concerned with the policy involved or that the results are injurious or otherwise, which may follow from giving effect to the language used. If the words used are capable of one construction only then it would not be open to the Courts to adopt any other hypothetical construction on the ground that such construction is more consistent with the alleged object and policy of the Act. In considering whether there is ambiguity, the Court must look at the statute as a whole and consider the appropriateness of the meaning in a particular context avoiding absurdity and inconsistencies or unreasonableness which may render the statute unconstitutional.
It is equally well settled that in interpreting a statute, effort should be made to give effect to each and every word used by the Legislature. The Courts always presume that the Legislature inserted every part thereof for a purpose and the legislative intention is that every part of the statute should have effect. A construction which attributes redundancy to the legislature will not be accepted except for compelling reasons such as obvious drafting errors. (See \026 State of U.P. and others vs. Vijay Anand Maharaj : AIR 1963 SC 946 ; Rananjaya Singh vs. Baijnath Singh and others : AIR 1954 SC 749 ; Kanai Lal Sur vs. Paramnidhi Sadhukhan : AIR 1957 SC 907; Nyadar Singh vs. Union of India and others : AIR 1988 SC 1979 ; J.K. Cotton Spinning and Weaving Mills Co. Ltd. vs. State of U.P. : AIR 1961 S.C. 1170 and Ghanshyam Das vs. Regional Assistant Commissioner, Sales Tax : AIR 1964 S.C. 766).
It is well settled that literal interpretation should be given to a statute if the same does not lead to an absurdity.

Citations : [2005 AIR SC 648], [2005 DRJ SUPP 80 518], [2005 JCR SC 2 71], [2005 JT SC 1 1], [2005 KLT SC 1 443], [2005 SCC 2 271], [2005 DRJ SUPPL 80 518]

Other Sources:

https://indiankanoon.org/doc/641119/

https://www.casemine.com/judgement/in/5609adf2e4b01497114129b9