I mean both of them are saints devoted to spirituality both of them follow brahmacharya etc i want to ask whether both have same significance in Hindu mythology? And what are the differences between sadhus and Nagas?
A sadhu (IAST: sādhu (male), sādhvī (female)), also spelled saddhu, is a religious ascetic, mendicant (monk) or any holy person in Hinduism and Jainism who has renounced the worldly life. ... Although the vast majority of sādhus are yogīs, not all yogīs are sādhus. The sādhu is solely dedicated to achieving mokṣa (liberation), the fourth and final aśrama (stage of life), through meditation and contemplation of Brahman.
Naga in Sanskrit means mountain, people residing in and around mountains are known as Pahadi or Naga. During ancient times, Naga Sadhus were taught to fight anti-Vedic invaders ferociously. Naga Sadhus were equipped with talwars, trishuls, gadas, teer dhanush and weaponry skills to protect Mandirs (मंदिर) and Maths (मठ). Naga Sadhus successfully protected Shiv Mandirs from invaders and mlecchas.
So a Naga Sadhu is basically a Sadhu only because both need to go through similar process initially. All sadhus have a common goal: attaining moksha (liberation), but Naga Sadhu has more definite role and has to go through stringent process, the process that is so unbearable, laborious, stiff and difficult that materialistic person becoming a Naga Sadhu is almost impossible.