Knowing each other in heaven is one of the great blessing we have to look forward to. This seems to be the whole point of Paul’s discussion of sorrowing for those who have died in Christ in II Thessalonians 4:13-18. In each verse he speaks of being reunited with those who sleep in Jesus. Because of this, we need not sorrow as others who do not have such a hope and therefore we can comfort one another with these words.
The Jews looked forward to being with Abraham, Isaac, and Jacob and all the prophets. Therefore Jesus said that there would be weeping and gnashing of teeth when they saw these great men in the kingdom while they themselves were being cast out. Jesus then said that the Gentiles would enjoy the presence of the prophets instead (Luke 13:28-29).
When Jesus met Martha after the death of her brother Lazarus, Martha expressed the hope of seeing her brother again in the resurrection. But Jesus said, “I am the resurrection,” telling her that she could see her brother again immediately if He so desired (John 11:21-27).