The Lord already had his 12 men (Matthew 10:1-4 KJV) preaching the gospel of the kingdom/ the kingdom of heaven is at hand and later Matthias replaced Judas being numbered with the eleven (Acts 1:25-26 KJV) restoring the number of them to 12 who were preaching a gospel and will in the future judge the twelve tribes of Israel (Matthew 19:28). So then you have to ask yourself:
Why Paul?
Why did the Lord have to appear to Paul Himself if this was all the same good news?
Why not just send one of the 12?
The 12 walked with Christ for over three years and judged Israel on twelve thrones after Pentecost.
It culminated in the destruction of the whole nation and the only ones saved out of it were the believers.
The command to go into all the world has continued since then by further apostles and prophets.
Paul was chosen as an example of longsuffering for believers of the nations.
Peter and the other apostles suffered the same, but Paul had many qualifications for the work which the others did not have, and his ministry was to the saved mainly.
However after saying all of that, and recognizing the Angel of the Lord with Peter, we see that Paul had the same.
People who look at men ought place their eyes upon Him who was with, upon, and in them, and see Jesus Christ as the one who was going into all of the world with His gospel.
Luk 13:34 O Jerusalem, Jerusalem, which killest the prophets, and stonest them that are sent unto thee; how often would I have gathered thy children together, as a hen doth gather her brood under her wings, and ye would not!
Luk 13:35 Behold, your house is left unto you desolate:
and verily I say unto you, Ye shall not see me, until the time come when ye shall say, Blessed is he that cometh in the name of the Lord.
Act 5:14 And believers were the more added to the Lord, multitudes both of men and women.)
Act 5:15 Insomuch that they brought forth the sick into the streets, and laid them on beds and couches, that at the least the shadow of Peter passing by might overshadow some of them.
Act 5:16 There came also a multitude out of the cities round about unto Jerusalem, bringing sick folks, and them which were vexed with unclean spirits: and they were healed every one.
LA