Ye Fan wanted to continue cultivating, but not Spiritual Energy.
If he continued to cultivate Spiritual Energy, he would have to undergo ascension and tribulations, which he didn't want to do so soon. At least, not until he could control multiple spatial boundaries.
What Ye Fan wanted to cultivate was life force. Now that he had grasped the knack for this cultivation, he would use ordinary people as the foundation for cultivation, transferring life force into his own body.
It's similar to the cauldron method used in cultivation, but not exactly the same. The cauldron method requires the opposite sex, while cultivating life force does not have such a restriction.
