If you tried to practise it without a good amount of fire resistance you would quickly find yourself burnt it a crisp!
Fortunately, with the fire immunity provided by his Dragon Soul, he didn't have to worry about such things. Dante had completed the first step, opening the acupoint and providing a Chanel for fire element energy to enter inside. But just because he had completed the first step didn't mean that his work was over, in fact, far from it.
At this point, all that was left inside of his acupoint was a storm of raging fire elemental energy.
If things were left as they were they wouldn't be of much benefit to Dante and in fact, would actually do more harm than anything.
Gathering the fire elemental energy together again Dante's mental power was stretched to its limit again as he began to compress the fire element together.
