When looking at the four Gospels and what was involved when Jesus called His disciples, there are many things involved but three stand out. I would not go so far as to say that discipleship only consists of these three things, but they are extremely important in our Christian walk.
The first thing Jesus did when calling his disciples was to tell them to follow Him. It boggles the mind to think of men engaged in their family business having a stranger approach them, call for them to drop everything and follow Him and they do it! Yet, this is exactly what happened. Those men who were fishermen by trade, and whose father depended upon them to run his business, simply walked away from their families and livelihood and followed Jesus.
Can you imagine Peter going home and telling Mrs. Peter that he had quit his job and was leaving to follow this new guy who walked along the beach? Can you imagine their father hearing he was losing the sons who enabled his business to function? Anyone who says discipleship is easy misses the very first aspect of it, which is the commitment to follow which implies leaving behind what had been most important in one's life.
Jesus did not only call His disciples to follow Him, He demanded they abide with Him day in and day out. Since Jesus had no mansion to dwell in, this abiding with Him consisted of sleeping under the stars many times along with harrowing nights in small boats during storms upon the Sea of Galilee. The only way His disciples could capture Jesus' heart, was for them to be with Him constantly and learn how He thought and did things.
Jesus not only taught His disciples, He required them to see how He did things, hear how He taught the people, feel how He manifested compassion and experience how He dealt with those who opposed Him. To receive this kind of learning meant being with Him constantly, not just for an hour once a week. The disciples lived with, learned from, observed and otherwise abode with Jesus until the end of His life.
The purpose of all the learning the disciples obtained was for them to go forth and carry on the ministry of Jesus Christ after His death and resurrection. The reason Jesus demanded His disciples follow Him and abide with Him was so they could learn how to live as He lived and do as He did. Jesus knew what was coming and part of His ministry was to raise up men who would carry on after He was gone.
It is incredible to think that Christianity started with one man who called twelve men who ended up ministering to thousands of people. It is amazing to realize that the billions of people who have become Christians the past two thousand years can be traced back to twelve men going forth and doing what they learned from Jesus from following and abiding with Him. Shall we do the same?