The welterweight bout between Errol Spence Jr and Manny Pacquiao will be for the Ring Magazine welterweight belt. It is certainly big fight as many consider the Ring Magazine as one of the most important belts to have.
In order for the Ring Magazine to issue a belt, it needs to be the best active fighters in the division to clash. It is safe to say that the winner of the Ring Magazine is the current best fighter since in order for it to happen the first and second ranked fighters should clash, if unable the third ranked fighter could get into the picture.
Errol Spence Jr currently holds two of the major belts in the division which is the WBC and IBF welterweight title so Spence is clearly the number one fighter in the division right now. As for Pacquiao, he just beat Keith Thurman to become the WBA belt but was later changed to champion in recess but as far as his ranking he might be third or even second if we just based on his resume for the division.
Many would say Terence Crawford is clearly the best welterweight or the number 2 but him fighting Errol Spence Jr could not happen anytime soon. Crawford also has not fought the names that Spence and Pacquiao beat. Crawford has an argument for being the top pound for pound fighter but in terms of welterweights he still lacks the big names.
What is interesting is if Pacquiao somehow beats Spence, he could make the argument of being the greatest fighter of all time. His career is already considered an all-time great with or without this fight but this fight is a fight that many expect him to lose. If he defies father time once more and beats an undefeated Errol Spence Jr, he will surely make an argument as the greatest boxer to ever live.