What does Mark 12:7 mean?
Mark 12:1 mentions that the landowner has planted the vineyard. It takes four years before a vineyard can be fruitful; for the tenants, that's four years of hard work with no contact from the landowner. In Jesus' time, in Galilee, rich men regularly buy up land and lease it to farmers while they live in another country. The landowners will send servants to collect some of the crops for payment. If the landowner disappears or abandons the property, it is legal for squatters to assume possession.This explains why the parable's servants think they can kill the heir and take over the land. They seem to assume that the arrival of the son implies that the original owner has died; the death of the rightful heir would free the land for taking by the servants. Of course, the tenants are gravely mistaken. The owner lives and has the right to ask the civil government to expel the tenants by whatever force is necessary.
At this point in history, about five hundred years after the Jews returned from Babylon and rebuilt the temple and the wall around Jerusalem, the people appear to follow God more closely than ever before. No one sacrifices their children to Molech (Jeremiah 32:35) any more. Baal and Asherah worship are left behind (Judges 2:13; 1 Kings 16:33). The people perform proper sacrifices and hold feasts and generally live lives more in line with the Mosaic law.
Unfortunately, this behavior is mostly hollow ritual and tradition, especially on the part of the religious leadership. The defining characteristic of true reverence for God isn't diligence in following rituals and laws, but a readiness to repent and accept Jesus as the Messiah, as John the Baptist taught.
Instead of honoring God as the source of every blessing, and recognizing their behavior as a sign of respect for God's position, the Jewish leadership withholds their hearts from God. In Jesus' parable, they are the tenants who kill the son. These religious leaders have remade Judaism so they receive the honor and the glory, just as the parable's tenants seek to receive all the wine.