“It is important to realize how significant this was for Jesus and his contemporaries. For the oriental, table-fellowship was a guarantee of peace, trust, brotherhood; it meant in a very real sense a sharing of one’s life. Thus, table-fellowship with tax collectors and sinners was Jesus’ way of proclaiming God’s salvation and assurance of forgiveness, even for those debarred from the cult. This was why his religious contemporaries were scandalized by the freedom of Jesus’ associations (Mark 2.16; Luke 15.2) – the pious could have table-fellowship only with the righteous.
But Jesus’ table-fellowship was marked by openness, not by exclusiveness. That is to say, Jesus’ fellowship meals were invitations to grace, not cultic rituals for an inner group which marked them off from their fellows …”
(James G. Dunn, Unity and Diversity in the New Testament, p. 176-177)