It lets you cheat on the first equipment cost you pay per turn, which is great to keep your responses quick and flexible
Not only does this mean the number of times you can activate the abilities are limited (by my count, Esper Dragons, the tier one deck that runs the most spells in standard, plays 25 instants/sorceries), but also that Disciple of the Ring is directly competing for the same resource as extremely powerful delve cards like Tasigur, the Golden Fang and Dig Through Time and also a nonbo with the new spell mastery mechanic
However his three toughness puts him well in range of most removal, so he's not at risk of becoming a Sheoldred-style threat that you have to tech around
From powerful creatures to game-changing spells, the possibilities are nearly endless
You can blink your entire board with cards like Glimmerpoint Stag, or give +2/+0 to everybody using Battle-Rattle Shaman