The Bible says some are called to be apostles (I Corinthians 12:28). Why then do we emphasize that no one fulfills the condition of being an apostle currently? Or is it a similar word but has a different meaning?
An apostle is an ambassador of sorts (i.e., one with official authority to speak for the person or nation being represented) and a disciple is a follower. So, all Christians would be disciples of Christ because we would all be following Christ. That would not be true of an apostle. If I went to a foreign country and misbehaved, I could easily hurt the reputation of my fellow countrymen, but that would be about the limit of it. However, if an ambassador misbehaves, there could be serious repercussions. The difference is that the ambassador has authority that is not carried by an average citizen.
Mark 3:14 and Luke 6:13 says that an apostle was a designation that was intentional and there are just a couple of passages that suggest that others were designated later. However, there is no succession plan or qualifications for designating an apostle other than those given in Acts 1:21-22. In that list, the minimum qualification was that they had to be with Jesus from the time of his baptism and also a witness of the resurrection. That would narrow down the field to just a few hundred people.
Even so, we are not actually without apostles now. Quite often we have a limited view of life mostly due to what we actually can observe. We may know someone who is the owner of a store. When the person dies, he is no longer the owner. Ownership passes along to someone else. We, therefore, think that someone ceases to be something just because they die and, therefore, all things associated with that person also have to pass to someone else.
One of the challenges that Jesus faced when talking to men is getting them to realize that the spirit realm is not interrupted by death. Jesus is still Lord (Romans 10:9), even though he died. Jesus said in Matthew 22:32 that God intended for us to understand that Abraham, Isaac, and Jacob were alive, even though they had died. Even so, the apostles did not cease to be apostles just because they died. The authority given to them was and still is binding.
We get the Word of the Lord through the written words of the apostles. They still live; therefore, their word is still binding. It is a lot easier now because we only have to look at the Word and anyone who disagrees with the Word is not to be believed or followed (Galatians 1:6-10). I Corinthians 1:21 also says that it was God's design that the word of salvation is spread by preaching. To people in the world that is a poor way to do it. The world likes to have flamboyant showmen. They also want to have a person to believe in. However, that very attitude was getting the Corinthian church in all sorts of trouble. In the first chapter, Paul chews them out because they are trying to hold on to specific teachers when they are supposed to be holding onto Christ. If we had modern apostles we would have the same issue; we would want to follow the people we see rather than the word that was confirmed to have come from God.
By having the Word delivered and confirmed through the power of real miracles, the apostles left us with a testimony that cannot be shaken. The only way to hold on to Christ is through the word that was delivered. Jude 3 says that the intent had always been that the word was to be delivered just the one time. That means that, after it was delivered, it was not going to change. The job of the apostles was to show everyone that the word they were delivering was from God. Once it was delivered, there is no continual need for apostles to prove that it came from God.