When he had the Dragon Soul before, he didn't know how to absorb it.

Now that he's truly absorbed the Dragon Soul, he realizes what a great opportunity he missed before.

At this moment, a golden Dragon Soul is resting near his Dantian, and all the Spiritual Energy in his body is enhanced by the Dragon Soul as it passes through the Dantian. This enhanced Spiritual Energy, containing dragon aura, then travels through his meridians to every part of his body, ultimately strengthening every inch of him—he should have become a Super Saiyan long ago, but the cancer cells held him back until now.

"The Ancestor was right, if you're sick, you need to treat it, no doubt about it."