I am a Christian but my friend has pointed out several contradictions in the Bible I when the women went to the tomb of Jesus I was hoping you could help me to resolve:
Matthew - Earthquake with angel sitting outside on the recently moved stone;
Mark - Stone already moved and a young man sitting inside;
Luke - Stone already moved with two men standing inside;
John - Stone moved. No one seen on first visit, but two angels sitting inside after two earlier visits.
Why does one story have two angels and another have one?
Have you ever been to a court and listen to multiple witnesses give an account of what they saw? Even when each person is being completely honest, their description will not match exactly. Why? First, people stand in different places, so what one person directly sees may not be what another person sees. Second, people rarely retell everything they witness. Most of us will provide an edited account emphasizing what we think is most important for the audience to whom we are describing the scene. Third, there can be a difference in time. People don't always arrive at an event at the same time, and so see different details.
Understanding this, let's look at each account of the tomb.
"Now after the Sabbath, as the first day of the week began to dawn, Mary Magdalene and the other Mary came to see the tomb. And behold, there was a great earthquake; for an angel of the Lord descended from heaven, and came and rolled back the stone from the door, and sat on it. His countenance was like lightning, and his clothing as white as snow. And the guards shook for fear of him, and became like dead men. But the angel answered and said to the women, "Do not be afraid, for I know that you seek Jesus who was crucified. He is not here; for He is risen, as He said. Come, see the place where the Lord lay. And go quickly and tell His disciples that He is risen from the dead, and indeed He is going before you into Galilee; there you will see Him. Behold, I have told you." So they went out quickly from the tomb with fear and great joy, and ran to bring His disciples word" (Matthew 26:1-8).
"Now when the Sabbath was past, Mary Magdalene, Mary the mother of James, and Salome bought spices, that they might come and anoint Him. Very early in the morning, on the first day of the week, they came to the tomb when the sun had risen. And they said among themselves, "Who will roll away the stone from the door of the tomb for us?" But when they looked up, they saw that the stone had been rolled away--for it was very large. And entering the tomb, they saw a young man clothed in a long white robe sitting on the right side; and they were alarmed. But he said to them, "Do not be alarmed. You seek Jesus of Nazareth, who was crucified. He is risen! He is not here. See the place where they laid Him. But go, tell His disciples--and Peter--that He is going before you into Galilee; there you will see Him, as He said to you." So they went out quickly and fled from the tomb, for they trembled and were amazed. And they said nothing to anyone, for they were afraid" (Mark 16:1-8).
"Now on the first day of the week, very early in the morning, they, and certain other women with them, came to the tomb bringing the spices which they had prepared. But they found the stone rolled away from the tomb. Then they went in and did not find the body of the Lord Jesus. And it happened, as they were greatly perplexed about this, that behold, two men stood by them in shining garments. Then, as they were afraid and bowed their faces to the earth, they said to them, "Why do you seek the living among the dead? He is not here, but is risen! Remember how He spoke to you when He was still in Galilee, saying, 'The Son of Man must be delivered into the hands of sinful men, and be crucified, and the third day rise again.'" And they remembered His words. Then they returned from the tomb and told all these things to the eleven and to all the rest. It was Mary Magdalene, Joanna, Mary the mother of James, and the other women with them, who told these things to the apostles" (Luke 24:1-10).
"Now on the first day of the week Mary Magdalene went to the tomb early, while it was still dark, and saw that the stone had been taken away from the tomb. Then she ran and came to Simon Peter, and to the other disciple, whom Jesus loved, and said to them, "They have taken away the Lord out of the tomb, and we do not know where they have laid Him."" (John 20:1-2).
Let's take it point by point.
Who came to the tomb? Matthew lists Mary Magdalene and another Mary. Mark lists Mary Magdalene, Mary the mother of James, and Salome. Luke says it was Mary Magdalene, Joanna, Mary the mother of James, and some other women. John only mentions Mary Magdalene. Were any of these accounts in conflict? Not really. None of them says only certain women were present. Each just list the ones important for the account they are about to tell. When we combine the accounts we find that present were Mary Magdalene, Mary the mother of James, Salome, Joanna, and at least one other unnamed woman (because Luke says "other women" which means more than one).
The guards. Only Matthew mentions the Roman guards who were present. This doesn't mean that Mark, Luke and John disagree with him. It just means that the guards weren't important in their account of what happened, so they skipped that detail.
The stone. All four mention that the stone was moved from the door before the women arrived. Only Matthew mentions how it was done: there was an earthquake and an angel rolled the stone back. How did he know (besides being inspired by God)? Remember the guards that only Matthew mentioned? The women couldn't testify regarding how the stone was removed because it happened before they arrived.
The angel at the entrance. Matthew mentions that the angel who rolled back the stone, sat on it and invited the women to enter the tomb and see that it was empty. The other three skip this event.
On entering the tomb. Luke mentions that they entered and were perplexed at finding it actually empty. The other three accounts skip this small fact. Luke then mentions that two angels appeared to them while they were in the tomb and one spoke to them. Mark mentions them seeing an angel who spoke to them, but his account doesn't say that there was only one angel. Mark does mention that the angel who spoke was on the right side, which could be taken as implication that there was someone on the left side. Neither Matthew or John mention what the women saw, or didn't see inside the tomb.
Who they told. John states that Mary Magdalene told Peter and himself. Luke says the women told the eleven apostles and the rest of the disciples. Mark says they told no one. And Matthew says they told the disciples. John and Matthew's account are a subset of what Luke records, so all three are in agreement. At first you might think that Mark's account is in conflict until you read further and find that Mary Magdalene, "She went and told those who had been with Him, as they mourned and wept" (Mark 16:10). Thereby we conclude that Mark meant that from the point of leaving the tomb to the time they found the disciples, they told no one what they saw. It is an important point, because it indicates that there were limited people involved at the beginning who might have altered what they women found. It is unlikely that someone came while the women were gone to alter any of the evidence because no one else knew what had happened.
What you find is that the accounts are in agreement concerning the details given. Where your friend is claiming a contradiction is in what each of the accounts do not say. He is assuming that because they didn't say something that this means it didn't happen. But such is merely speculation and not properly logical.
Let me illustrate this. Brad comes up to you and says "Jeff drives a Taurus." Suzy tells you, "Jeff drives a dark green sedan." Joe says, "Jeff's car is so dark, it is nearly black." And Bob tells you, "There is a dent in Jeff's car and it really could use a wash." Are these four people contradicting each other? Obviously not even though each of them gave different details.