In the parable, the son is sent "last of all" — not meaning no more messengers ever, but that the Son is the final opportunity before judgment falls on the leaders. Jesus is greater than every prophet: they are slaves; he is the beloved Son.

Jesus's sending as the "last" messenger doesn't mean no prophets/apostles after him (Luke predicts Jesus will send prophets and apostles). Rather, the Son is the final chance before judgment on these specific leaders. The Father says "they will respect my son" — not because God actually thought they would, but to highlight the extremity: killing slaves is bad enough, but killing the beloved Son is insane. John 5: "You should honor the Son even as you honor the Father." Subtle theology: in Isaiah 5, "beloved" refers to God; in Mark 12, "beloved" refers to the Son — an identity connection between Father and Son, consistent with Mark's subtle Christology throughout. The vine growers' motive for killing the son: "the inheritance will be ours" — wanting control, which is the ultimate motive for rejecting Christ's lordship.