The death of Jesus is a puzzle to many, because there is so much evidence for Him being alive after the crucifixion.  In order to disprove the resurrection, some people say that Jesus did not really die.  John would have heard those ideas but he witnessed the events at the end of crucifixion day.  He saw that Jesus was dead and so did the soldiers.  The evidence of Jesus’ death was so clear to His executioners that they did not bother to break His legs (the practice which accelerated death by traumatic stress and blood loss).

John prefaced this by saying that this was the Special Sabbath at the end of the Passover.  This festival recalled how a lamb was slaughtered, its blood daubed on the doorframe of each believing household and its flesh eaten.  When that happened, the angel of death ‘passed over’ the house and did not bring destruction.  The sacrifice of the lamb saved the people who sheltered under its blood and were strengthened to leave the captivity of sin. In Exodus 12:46, Numbers 9:12, and Psalm 34:20, God insisted that the sacrificial lamb must not have any bone broken.  Jesus is our Passover Lamb.
 
However, just to prove that Jesus was dead, one soldier jabbed his spear upwards into Jesus’ side.  It was a large wound into which Jesus would later invite Thomas to place his hand.  There was no doubt that His heart had stopped some time before as the cellular and plasma components of His blood separated and were seen to flow from Christ’s body.  So, John had the right, as an eyewitness, to conclude that Jesus was fully dead; and therefore that the resurrection was truly God’s miracle, and that Jesus is still alive.  John understood that salvation comes by repenting of sin and believing in the death of Jesus Christ and His resurrection.  His death was to take away their sin, and His resurrection was to prove His triumph over death and the devil (John 20:24-30).
 
Although some people seem satisfied to have religious feelings, the gospel writers were clear that it is necessary to believe in the facts of Christ’s death and resurrection.  Those were the real events in which Jesus dealt with our sin.  So John’s message still speaks to us today.  It urges us to believe in the Jesus who died for our sin and was raised for our justification (Romans 4:25).  That was the faith for which many of the Apostles were martyred, and by which every believer is saved.  There is no other gospel which is true to the Bible or to Jesus.  It therefore matters very much what we believe.  So, those of us who know and trust Jesus also have a responsibility to share the same gospel with our friends and colleagues.