We know that during the Crucifixion, Jesus was only on the cross for three to six hours and then taken off. Crucifixion is in fact a very slow, painful death that usually takes 3 days not 3 hours. To speed things along, you can break the legs, thus remove the support and put more pressure on the heart. Both people on either side of Jesus had their legs broken, but Jesus did not, so the question arises of how did he die so quickly? No one examined Jesus’s body to determine death, instead it is stated that a soldier 'pierced his side with his spear, and blood and water gushed out'. (John 19:34) Now how is that a sign to prove death? It proves the opposite. The heart pumps the blood around the body, when the heart stops, so does the pumping action. So what should have happened is a small amount of blood should have trickled out if he was dead, but if he was still alive, only then would blood gush out.
His body was taken to a very spacious tomb and then treated with a hundred weight of aloe - a healing agent of the time. Why was there a need of such a huge amount? We then see that the stone slab covering the tomb had to be removed. If Jesus was dead, then why did he need to get his physical body out of the tomb?
We then see that Jesus disguised himself as a gardener and travelled in secret to meet his disciples, why? What should have happened is that Jesus should have gone to the Jews and openly taunts them that you tried to kill me, but God saved me and I am now on the right hand side of God etc, but instead we see Jesus appearing to be scared of the Jews, afraid of being caught, why? Unless he was really alive, and knew that if he gets caught, then the Jews would put him back on the cross.
People started talking about Jesus rising, and we hear about the doubting Thomas. Thomas thought that he was a ghost and so Jesus met him as said
Behold my hands and my feet, that it is I myself: handle me, and see, for a spirit hath not flesh and bones, as you see me have
So Jesus put his mind to rest and asked him to handle him and find out that he was not really dead, he was not a ghost, instead, he was alive, just like Thomas. To further this point, Jesus then went and ate 'broiled fish and honeycomb' (Luke 24:42-43) with them.
After some time, he recovered and then went up the mountain, but instead of rising to Heaven, he went over the other side and went in search of the lost sheep of the house of Israel, who unlike the Jews in Israel, these Jews accepted and welcomed him.
So this is how we understand what really happened. Of course, if this is correct, then as St Paul said "If the Christ be not risen (from the Dead) then our preaching is in vain and your faith also vain" (I Corinthians 15:14).
In other words, all the Christian teachings of resurrection, redemption, salvation etc. are based on Jesus dying on the cross. But these are all teachings which were introduced by St. Paul, and not Jesus. These are not Jewish teachings, which Jesus taught.
For further information please look at the following link: http://www.alislam.org/topics/jesus/