Makarov used his last ounce of energy to cast a powerful magic, the Fairy Law, to wipe out majority of Alvarez Empire soldiers. His sacrifice caused grief in the hearts of every Fairy Tail mages in the battlefield and at the same inspired them to finish their fight against Zeref and his henchmen.
Recap of Fairy Tail 506: Broken Bonds
-Chapter opens with Erza and Mavis saddened with the loss of Fairy Tail master Makarov. Mavis reminisces the first time she saw Makarov, revealing that she's actually the one who gave that name to his future protégé.
-Laxus, the grandson of Makarov, comes to comfort a grieving Mavis, trying to convince the first Fairy Tail master to continue the fight not only for the sake of Ishgar's mages but for the memories of his fallen grandfather.
-Erza takes a bow one more time in front of the petrified body of Makarov, uttering these words "To be able to grow up as your child...I was happy beyond words."
-Cut to the scene of Erza and Zeref talking about the aftermath of Makarov's Fairy Law attack. The Scarlet Despair reports that 70 to 80 percent of their army has been wiped out by that spell, although all members of the Spriggan 12 remain alive. She claims that momentum is still on their side, despite Makarov's suicide attack.
-Back to ongoing showdown between Gray and E.N.D (Natsu). Natsu starts it off with powerful claw attack. Gray blocks it and launches an ice beam towards Natsu. The Dragon Slayer takes a direct hit but recovers right away. He then breathes a massive fireball, and again Gray blocks it with a wall of ice.
-Gray and Natsu realize that they are evenly matched. In an attempt to finish their battle once and for all, they both decide to end with one powerful blow (ala Naruto vs. Sasuke). Just when they are about to hit each other, Erza comes out of nowhere and catches both fists, scolding his two Fairy Tail brothers "What do you two imbeciles think you're doing."
Prediction of Fairy Tail 507: Voice
I feel Mavis will start to make her move and show to everyone - including the naysayers - how powerful she really is. The chapter's title 'Voice' might be pertaining to Mavis unifying Fairy Tail along with other Ishar mages for a common purpose: to defeat Zeref and Alvarez Empire.
With regards to what's going on with Gray and Natsu, I can see Erza finally finding ways to repair the bond connecting his two Fairy Tail members. Put some grain of salt here, but I have a strange premonition that we will finally see Erza going head-to-head with Eileen.