First, it was able to raise the innate grade of a soul. The innate grade of a soul was the starting level a newly birthed child would have. On the mortal plane, this was practically disregarded entirely.
Dyon's innate soul grade was at the 4th level because he didn't need to actively cultivate his soul to already be at the peak meridian formation level. The only reason his soul hadn't been at that level when he initially entered the martial world was because his body was too weak. But, after his body strengthened, his soul easily reached that rank.
This was already absolutely shocking as it was thought that the absolute peak possible for an innate soul grade was the 3rd, but Dyon was an entirely level above this.
This said, innate soul grades were even more important on the immortal plane and were not disregarded. If a mother drank this elixir while her child was in her womb, then the child's nascent soul was raised by an entire grade.