Just saying how much stronger he would become after killing the Celestial of Power, the Celestial of Fire, and becoming the Celestial Supreme made the Celestial of Light make up his mind not to let this opportunity go at all costs. He has been fantasizing about it for a long time. But this time he might really achieve it.
It also isn't all about the allure of power. He made a blunder early into the rite of passage when he falsely accused the Shadow of Despair and amassed an army against him. That blunder will be the death of him as soon as the Shadow of Despair comes to the divine plane so he has to acquire power to ensure his survival.
The gods began to argue. Then they began insulting each other. That quickly devolved into the exchange of blows. They were soon at each other's throats.
