Wei Shengxin probably wanted to make a move against him as well; he simply had hesitations for the time being.
If Wei Shengxin hadn't taken action now, it meant that he hadn't broken through to Martial Saint yet.
Once Wei Shengxin broke through to the Martial Saint realm, it was very likely that he would actively seek out Su Changkong's whereabouts to settle scores. Given this, it was better to take the initiative to approach him!
Su Changkong was indeed worried about Wei Shengxin.
From Ji Xuexiao, he had learned of the strengths and weaknesses of a Martial Saint. If Wei Shengxin managed to achieve Martial Saint through his own cultivation and then refine the Divine Seed he controlled, he would possess two Divine Skills and be in the second layer of the Entering Saint realm!