This might be a question better suited for /r/christianity but I will go ahead and give a brief explanation.

The book of Acts (Short for Acts of the Apostles) which outlines what the followers of Jesus did in the time after Jesus departed, Peter, the lead disciple in Jesus' absence, has a vision in Acts 10:9-16.

9 The next day as Cornelius’s messengers were nearing the town, Peter went up on the flat roof to pray. It was about noon, 10 and he was hungry. But while a meal was being prepared, he fell into a trance. 11 He saw the sky open, and something like a large sheet was let down by its four corners. 12 In the sheet were all sorts of animals, reptiles, and birds. 13 Then a voice said to him, “Get up, Peter; kill and eat them.” 14 “No, Lord,” Peter declared. “I have never eaten anything that our Jewish laws have declared impure and unclean.[a]” 15 But the voice spoke again: “Do not call something unclean if God has made it clean.” 16 The same vision was repeated three times. Then the sheet was suddenly pulled up to heaven.

Essentially, Mosaic Law which banned the eating of Pork was justified in being eaten when this book, and other letters were taken to be biblical cannon. Keep in mind that many early Christian sects did not adopt this practice until well into the second and third centuries.

I've heard several arguments from textual scholars over the years that have said that part of what lead early Christians to adopt this new practice was part of a recruiting tactic, since many non-Jewish people had been having their own eating habits for several millennia, and would not be as east to convert if there were serious restrictions.