The Pharisees' reasoning
The Pharisees did not believe Jesus would rise on the third day. They knew that Jesus had prophesied it would happen, and they wanted to prevent anyone from believing the prophecy had been fulfilled through deception on the part of the disciples (by stealing the body).
The Pharisees did not simply want to kill Jesus, they wanted to destroy His movement. Having Him put to death by crucifixion would be humiliating, and having Him put to death by Rome would intimate that His teachings were opposed by the might of Rome. The slow, tortuous death by crucifixion also afforded ample opportunity to mock Him as He suffered (see Matthew 27:39-43).
They realized that if Jesus were thought to have risen from the dead, it could further strengthen His movement (it did). This is what is meant by "This last deception will be worse than the first".
If the Pharisees genuinely believed Jesus was the Son God who would conquer death...of course they wouldn't have posted a guard! What chance would the guards have against the power of God? It was because the Pharisees did not believe in Jesus that the posting of the guard (to prevent theft of the body) made sense in their twisted, doubting minds.
The disciples' struggle to believe
That the promised Messiah would be put to death by Rome, rather than conquering Rome, was so foreign to contemporary thought that many of Jesus' followers genuinely entertained doubts when they saw Jesus arrested and put to death. Forasmuch as He had told Him it would happen, they were shocked and grieving.
It is not that the Pharisees understood Jesus' prophecy and the disciples did not, rather:
- The Pharisees didn't believe in Jesus before He died and still didn't believe after He died
- The disciples did believe in Jesus before He died and were struggling to believe after He died
The apologetic value of the story of the guards
Posting a guard at a tomb was not standard practice; it was specifically to prevent the theft of Jesus' body--which the Pharisees realized could fuel Jesus' movement--that guards were posted in this case.
Although the Pharisees did believe in the resurrection (the Sadducees did not), they believed it would happen only at the end of the world, and certainly not begin in their own lifetimes.
As William Lane Craig (and others) have pointed out, the argument between the Pharisees and the believers in Christ presupposes the empty tomb:
Christian: 'The Lord is risen!'
Jew: 'No, his disciples stole away his body.'
Christian: 'The guard at the tomb would have prevented any such
Jew: 'No, his disciples stole away his body while the guard slept.'
Christian: 'The chief priests bribed the guard to say this.' (source)
As Craig further points out:
The sleeping of the guard could only have been a Jewish development, as it would serve no purpose to the Christian polemic (ibid)
The argument would have never progressed this far unless both sides agreed:
- The tomb was empty &
- There was a guard posted
The Pharisees had no reason to agree to those points unless they were incontrovertibly true.
The reliability of Matthew
My work on the Synoptic Problem & the authorship of the Gospels leads me decisively to the conclusion that the Gospel of Matthew was written in or near Judea within a few years of Easter. If this is true, Matthew's defense of the resurrection would be ineffective--as his evidence could be easily rebutted by people who were there and knew what really happened--unless the claims he made about the tomb & guards were actually true.
This is why the account of the guards is found only in Matthew--Matthew's audience (in/near Judea) has the ability to fact check this part of the story. Mark's audience in Rome, Luke's audience in Greece, and John's audience in Ephesus, would have no ability to validate the story about the guards, so the account about the guards would at best be a distraction from the main point they were trying to make. But for Matthew, writing to the local population, the story about the guards was potent, verifiable evidence of the veracity of his claims.
The Jewish leaders had every incentive in the world to produce a crucified body and squash the nascent Christian movement. The fact that they were unable to do so stands resolutely in favor of the view that Jesus really was buried in a tomb and the tomb really was found empty a few days later.
Matthew could only get away with his claims about the empty tomb & the guards if:
- Everybody in the area knew it was true OR
- The text was written so long after the fact that the people familiar with the events were dead.
This is why atheists work so hard to claim that the Gospel of Matthew was written a generation or more after Easter. For my work demonstrating that the Gospel of Matthew was written by the apostle Matthew well within the lifetime and geographic reach of eyewitnesses, see this video series: Who When & Why - the Writing of the Gospels