Jesus tells the parable in direct confrontation with Jerusalem's leaders. They understand that the story is directed against them.
The vineyard is a familiar image for Israel, while the repeated sending of servants naturally evokes God's long history of sending prophetic messengers.
Isaiah 5 portrays Israel as the LORD's vineyard. The Old Testament repeatedly recounts God's sending of prophets whom rebellious hearers reject.
Mark's phrase 'beloved son' also recalls the Father's declarations at Jesus' baptism and Transfiguration.
The owner sends servant after servant, but the tenants mistreat or kill them. Finally, having one beloved son, he sends him with the expectation that they will respect him.
The narrative draws a categorical line between the many servants and the one Son, who is also the heir. Jesus thereby places his own mission as the climactic divine sending.
Son language by itself need not mean deity, but this parable gives Jesus' sonship exceptional salvation-historical significance.
He is not another prophet in the sequence. He is the unique beloved Son and heir sent after the servants, fitting Mark's larger presentation of Jesus' unique relation to God.
The religious leaders perceive that Jesus has spoken the parable against them and seek to arrest him.