Part One: The cost of discipleship
In my opinion, the greatest disciple of the 20th century was Dietrich Bonhoeffer. He was obedient even unto death, and martyred himself not only for Christ, but for the body. He even wrote the definitive book on the subject, “The Cost of Discipleship.” Every Christian should read his book.
In his book, he writes, “. . .only he who believes is obedient, and only he who is obedient believes.”  For faith to be possible is a case when those two propositions are equal and true. We delude ourselves if we think we can have one without the other. In fact, it would be unbiblical.
Dietrich further writes, “. . .faith is the condition of obedience. In exactly the same way in which obedience is called the consequence of faith, it must also be called the presupposition of faith.” If we are to believe, we must first obey a command. The first step of obedience makes Peter leave his nets and later get out of the boat .
A disciple is a follower of Christ. The word disciple translated from the Greek word Mathetes, means more than a “student” or “learner.” Jesus was quite explicit about the cost of following Him.
So likewise, whosoever he be of you that forsaketh not all that he hath, he cannot be my disciple. [Luke 14:33 KJV]
Then said Jesus unto his disciples, If any man will come after me, let him deny himself, and take up his cross, and follow me. [Matthew 16:24 KJV]
The terms Christian and Disciple are related but not synonymous. They called Jesus followers “disciples” long before they ever called them Christians. Their discipleship began with the call of Jesus and required them completely to exercise their will to follow Him . Not all of Jesus followers were able to make such a commitment . Even today. The word Christian means, “belonging to Christ” and was first used as a derogatory term (just like they do today). The original meaning of the term Christian was a pejorative and finds some support in 1 Peter 4:16.
Can anyone really be a true disciple of Christ? We all fail. Read the Beatitudes  We just finished that study. Can any of us adhere to them all without fail and any number of the commands given in the Bible? (That’s rhetorical) However, this is where grace comes into play. We can only do our best and repent when we fail. . .and we will fail. . .daily. Now we can be followers of Christ and not be a true disciple, if we are to believe Christ and take Him at His word. We can be Christian disciples and Paul describes the reality of being a Christian disciple in Galatians 2:20.
I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
 The Cost of Discipleship page 63
 Page 64
 Matthew 9:9
 John 6:66
 Matthew 5:1-11