History of Purpose

Overview

Purpose is a Legendary weapon: Scout Rifle (Lightweight Frame), Kinetic, kinetic slot.

Curated roll per the fan wiki: Extended Barrel, Smallbore or Fluted Barrel; Slideshot or Hip-Fire Grip; Explosive Payload. Fire rate 200 RPM. Introduced in Season 2 (Curse of Osiris-era). Its default shader matches Benevolence of the Nine.

Acquisition

Trials of the Nine rank-up package from the Emissary of the Nine (Season 2 Trials of Osiris). Bungie's item text says to "complete Trials tickets and earn rank-up packages from the Emissary of the Nine", which is the Trials rank-up reward track. Older and newer sources describe this differently, so check in game for the current rotation.

This is a legacy-style reward weapon. It is not a craftable or Adept weapon as far as the sources show, and sunset status was not stated by the sources I opened (the fan wiki is the main source). See also Emissary of the Nine and the Crucible for the PvP context.