EDIT: 05 Dec 2018
Per an early December 2018 game update:
The "Lest Ye Be Judged" Trophy/Achievement can be completed by visiting Xurhttps://www.bungie.net/en/News/Article/47489
Xur is available from the Friday daily reset through the weekly reset on Tuesday. https://whereisxur.com/
Confirmed by geordiedeviant: talking to Xur is all that is required to unlock the achievement.
If the achievement doesn't unlock, log out through the Destiny menus (switch profile, perhaps) and log back in.
EDIT: As of September 2018, Trials of the Nine is not an active event, likely for all of Destiny's Season 4. Once an announcement is made regarding Trials being available again, I'll update the solution. In the meantime, this achievement is unobtainable.
Win one match to get access to a new social space. Travel there and talk to the Emissary of the Nine to pop the achievement.
You must have completed the campaign, Shaxx's Call to Arms milestone at least once, and be 260+ power to have access to Trials, which runs from 1pm est Friday through the reset at 5am est Tuesday.
Also note that Trials does not offer matchmaking so you must have a fireteam of four members all of whom meet the criteria in order to play.
If you're looking for players to attempt this with, I suggest checking out http://www.destinylfg.net or http://www.reddit.com/r/fireteams