Sword of Truth and Justice turns a successful combat hit into lasting growth. The equipped creature gets +2/+2 and protection from white and blue. When it deals combat damage to a player, you put a +1/+1 counter on a creature you control and then proliferate, letting one hit improve several counter-based resources at once.
The order is useful. You can place the first +1/+1 counter on a creature that had none, then choose that creature for proliferation and add another. Existing counters on other creatures, planeswalkers, or players can also be increased. A counter deck may therefore gain much more than two counters on its attacker from one connection.
Evasive creatures and repeatable attacks help make the trigger dependable. Cloud, Midgar Mercenary can double the attached Sword's trigger while equipped, and double strike can create another trigger in the second combat damage step. Planeswalker decks can use proliferation to build loyalty without spending additional activations, provided those planeswalkers already have loyalty counters.
Protection can help the carrier get through white or blue blockers, but it also affects your own spells and attachments of those colors. Check existing Auras before equipping. The Sword still needs combat damage to a player, so simply attacking or damaging a creature will not generate counters. In a deck with several kinds of counters already in use, it provides a combat plan that improves the rest of the board while growing the attacker itself.
