“And it came to pass, that, as Jesus sat at meat in his house, many publicans and sinners sat also together with Jesus and his disciples: for there were many, and they followed him.”
While Jesus was having dinner at Levi's house, many tax collectors and sinners were eating with him and his disciples, for there were many who followed him — the dinner at Levi's house is the kingdom's social vision in action: many tax collectors and sinners eating with Jesus and the disciples. The word sinners (hamartōloi) in this context refers not to the morally worst but to those who were considered outside the boundaries of covenant faithfulness by the religious establishment — people who did not observe the purity laws, who worked in degrading occupations, who were not Torah-observant. Jesus eats with them, which in the ancient world communicated acceptance, solidarity, and covenant relationship.
Church Fathers on Mark 2:15
After that the Lord taught at Capernaum, He went to the sea, that He might not only set in order the life of men in towns, but also might preach the Gospel of the kingdom to those who dwelt near the sea, and might teach them to despise the restless motions of those things which pass away like the waves of the sea, and to overcome them by the firmness of faith.
Or else, after the miracle, He goes to the sea, as if wishing to be alone, but the crowd runs to Him again, that thou mightest learn, that the more thou fliest from glory, the more she herself pursues thee; but if thou followest her, she will fly from thee. The Lord passing on from thence called Matthew.
Thus then Levi, which means Appointed, followed from the custom-house of human affairs, the Word, Who says, 'He who doth not quit all that he has, cannot be My disciple.'