Why is copper matte put in a silica-lined converter?

Copper matte contains $Cu_{2}S$ and $FeS$. Copper matte is placed in a silica-lined converter to remove the remaining $FeS$ and $FeO$ present in the matte as slag $(FeSiO_{3})$. Silica $(SiO_{2})$ acts as an acidic flux to remove the basic impurity $FeO$. When a hot air blast is blown,the following reactions occur:
$2FeS + 3O_{2} \longrightarrow 2FeO + 2SO_{2}$
$FeO + SiO_{2} \longrightarrow FeSiO_{3} \text{ (slag)}$
$2Cu_{2}S + 3O_{2} \longrightarrow 2Cu_{2}O + 2SO_{2}$
$2Cu_{2}O + Cu_{2}S \longrightarrow 6Cu + SO_{2}$