The Spiritual Qi was like dust particles surrounding us. Neither touchable nor seen, they exist but don't at the same time. But everything changed the moment this particle came into the body of a cultivator.
Like how gases get condensed and turned into vapor, then become a liquid, everything comes in steps. And by using the cultivation technique created by Qin Lan in his free time, the dust-like particles slowly gathered together before being absorbed into his core in an orderly manner.
But absorbing the Spiritual Qi was just a beginning.
His body would have to be the vessel capable of holding these particles together until they formed into energy. The energy will then be released back to his body to refines his flesh. This was the meaning of Flesh Refining Realm.