Natsu and his team were exhausted to no ends as they climbed the last 100 stairs, leading to the Shrine of Gods. At first they wouldn't even imagine coming up here, but they had to come here for 3 main reasons, the first being, that Kazu was also thinking of coming to this place, and they wanted to stop that man from bringing any harm to the Shrine of Gods. Kazu had time and time again proved that he is not a man worthy of trust, being young and indecisive, he had been led astray by the Master of corrosion, so he has to be dealt with.
The 2nd reason being that they wanted to warn the Light Gods about the scheming and planning, the Master of Corrosion had started to do against them.