5:5 A certain man was there, who had been sick for thirty-eight years.
5:6 When Jesus saw him lying there, and knew that he had been sick for a long time,
he asked him, "Do you want to be made well?"
5:7 The sick man answered him,
"Sir, I have no one to put me into the pool when the water is stirred up,
but while I'm coming, another steps down before me."
5:8 Jesus said to him, "Arise, take up your mat, and walk."
5:9 Immediately, the man was made well, and took up his mat and walked.

Now it was the Sabbath on that day.
5:10 So the Jews said to him who was cured,
"It is the Sabbath. It is not lawful for you to carry the mat."
5:11 He answered them,
"He who made me well, the same said to me, 'Take up your mat, and walk.'"
5:12 Then they asked him,
"Who is the man who said to you, 'Take up your mat, and walk'?"
5:13 But he who was healed didn't know who it was,
for Jesus had withdrawn, a crowd being in the place.
5:14 Afterward Jesus found him in the temple, and said to him,
"Behold, you are made well. Sin no more, so that nothing worse happens to you."
5:15 The man went away, and told the Jews that it was Jesus who had made him well.

5:16 For this cause the Jews persecuted Jesus, and sought to kill him,
because he did these things on the Sabbath.
5:17 But Jesus answered them, "My Father is still working, so I am working, too."
5:18 For this cause therefore the Jews sought all the more to kill him,
because he not only broke the Sabbath, but also called God his own Father,
making himself equal with God.

Take up your bed and walk!
Obeying this command is much like water baptism as it was intended. It should be "I believe therefore I obey". Obedience is an indication of faith. Rather than "I obey in order to be saved", in which doing particular things like getting wet or carrying your mat become the object of faith rather than the indication of faith.

I infer that Jesus purposely gave him this command in order to bring up the Sabbath controversy. Water baptism was to be an outward sign distinguishing the Christian from the rest of society. Carrying your mat on the Sabbath would also make a Jew stand out.  Though it is not explicitly stated in the Law, God elaborates on the Law through the prophet Jeremiah saying, "This is what the LORD says: Be careful not to carry a load on the Sabbath day or bring it through the gates of Jerusalem.  Do not bring a load out of your houses or do any work on the Sabbath, but keep the Sabbath day holy, as I commanded your forefathers." Jer 17:21,22 But the Jews often don't take into account the sense in which such things are written, but rather interpret in a very literal and legalistic manner, missing the spirit. The load that the man carried was not his mat but his infirmity. Being able to carry his mat at all would have been a get release from such bondage. And thus Jesus released him not only of the burden of his infirmity, but allowed him with pleasure to carry his bed away. He was going home with all his possessions and free from his infirmity. Now isn't that in the spirit of what is written? But the heartless religous leaders were all caught up in the legalism of it. Where were they when the waters stirred? Why is it that they wouldn't even help this man into the pool? They lacked to humility to recognize their blatant hypocrisy, as is the case for many people.

Sin no more!
Walking implies a certain lifestyle.  A lifestyle of sin brings only corruption and death. To be lame for 38 years would be considered bad enough, but that is nothing compared to the effects sin can have. What Jesus attempted was to make the man aware of his need for spiritual healing through the forgiveness of sins and through spiritual regeneration.  He preached repentance from sin. Such a message may be rare today in modern Evangelicalism dominated by antinomial theology in which little correlation is made between a person's behavior and their salvation status. And some of the early Christians were even deceived on this point to whom Paul wrote:

"Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God." 1Cor 6:9,10

The man went and told on Jesus.
I have the impression that this was done in somewhat Judas-like fashion. He was probably humiliated at Jesus' implication of him being a sinful man and being told to sin no more. The humiliation of physical suffering can develop humilty, but it can also develop bitterness if the person is proud. It was commendable that Jesus found him in the temple. But the man seemed ungrateful, perhaps not even seeking the Lord to thank him and only interested in passing the blame of this accusation incurred upon him for carrying his mat on the Sabbath. He seemed insensitive to the additional persecution he was incurring upon the Lord by telling the religious leaders. For he was under no obligation to tell them who healed him.  In contrast to this I will again point out the Centurion of Luke 7 who avoided having Jesus come to his house to heal his servant. One of the factors that no doubt led him to such a decision was that in love he wanted to avoid Jesus being viewed as a Roman collaborator and open him up to undue criticism.

The Sabbath Question
"My Father is always at his work" And yet it is written that God rested on the 7th day, from which the 4th commandment concerning the Sabbath rest is derived. Under the Mosaic Law violation of the Sabbath rest incurred the death penalty. (Kind of a permanent rest!) "Whoever does any work on the Sabbath day must be put to death." Ex 31:15 Which was one basis for putting Jesus to death. But again the Jews misunderstand the spirit of what is written. We know now that the Sabbath was symbolic of the rest we have in Christ which Hebrews 4 elaborates upon. The Jews were to act out that symbol through the Law. But the spirit of the Sabbath is rest. God works to provide us rest. Jesus healed the man to provide him rest from his affliction. But these works are to provide rest for others.

Let us by analogy consider the Christian life. It is written that "when a man works, his wages are not credited to him as a gift, but as an obligation. However, to the man who does not work but trusts God who justifies the wicked, his faith is credited as righteousness." Rom 4:4,5 And thus salvation is given graciously rather than earned through works. If a person views works as necessary in order to obtain or maintain one's salvation then they cannot say that they have entered into God's Sabbath rest. But there are works associated with the Christian life. We labor to provide rest for others just as the Lord did and as the Lord is doing through us. But such works are in a different category from those from which we rest.

Practically speaking how should the Jews have played out the Sabbath symbolism? By paying special attention to the needy providing them rest even if it means that some, not so needy, have to work. Jesus goes so far as to mock their hypocrisy saying, "If any of you has a sheep and it falls into a pit on the Sabbath, will you not take hold of it and lift it out?  How much more valuable is a man than a sheep! Therefore it is lawful to do good on the Sabbath." Matt 12:11,12 "Good works", in the sense in which he is speaking here, are not a part of the "any work" spoken of in the Sabbath Law. Not taking into account the spirit of what is written can result in such deviant applications of the Bible as is apparent among the religious elite throughout history.

The Deity of Christ
Though it is true that at times the Bible speaks of Israel being likened to God's children in an allegorical sense, and Paul makes reference to  mankind being the offspring of God again in an allegorical sense, but Jesus spoke of himself as being uniquely the Son of God. And he elaborates on his relationship with the Father for the rest of the chapter. This is a major theme in the gospel of John starting in chapter 1 where he is equated with God. And we saw in John 3 that he calls himself the only begotten Son. Jesus is the Son of God not in the same sense as Christians today reckon ourselves sons of God. Jesus is unique, having the same nature as God the Father and yet being a separate individual.  The implication of his teachings concerning his unique relationship with the Father was unmistakeably heretical from the point of view of his enemies. They did believed that God had a Son, but they didn't believe Jesus was him. The book of Proverbs 30:4 says "Who has gone up to heaven and come down? Who has gathered up the wind in the hollow of his hands? Who has wrapped up the waters in his cloak? Who has established all the ends of the earth? What is his name, and the name of his son? Tell me if you know!" What has been hidden in ages past has now been revealed. Today we do know the name of his son. Furthermore at his trial he was asked by the high priest "Tell us if you are the Christ, the Son of God."Matt 26:63 thus revealing that the Jews believed the Messiah (the Christ) to be the Son of God. And we saw Nathanael of John 1:49 say, "you are the Son of God; you are the King of Israel." again revealing Jewish beliefs that God had a Son and that he was the true King of Israel.