Every Christian recognizes an apostle means someone who was sent by God. But not every Christian believes God makes apostles any longer.
Yes, they say, God gives people certain duties and sends them forth. Yes, it sounds an awful lot like an apostle. But they’re not apostles. They’re called missionaries. Whereas apostles—real apostles—only existed in the first century. They were commissioned by Jesus personally, back when he walked the earth. That’d be the Twelve.
And Paul. We gotta make an extra-special case for Paul. ’Cause Jesus made a special trip back to earth to commission Paul.
And Barnabas. Not sure when Jesus called him to be an apostle, but the scriptures call him one. Maybe he was one of the 72 people whom Jesus sent to proclaim the Kingdom. Okay, so assuming the Twelve were included, and Paul’s an extra, that’d make 73 apostles. But no more.