Tang Jun made it clear that he would grant Lei Jie one wish out of respect for the fact that they had the same mother, and for that person who had given him warmth when he was a little kid.
However, he had also made it very clear that this wish didn't include showing mercy to Lei Jie in their battle later.
For Lei Jie, his arrogance prevented him to lowering his head before Tang Jun to apologize or even beg for mercy. If not, there wouldn't even need to be a contest between the two of them and he would have been ruined right away. He wouldn't have the chance to reach the nascent soul advanced stage, let alone the immortal soul stage.
The giant hole in his mindset and mentality could even cause his battle prowess and the power of his mantras to gradually decline.
Therefore, his battle with Tang Jun was necessary and bound to happen.
