estaban sirviendo
Imperfecto progresivo para el sujeto ellos/ellas/ustedes del verbo servir.

servir

A ellos se les reveló que no se estaban sirviendo a sí mismos, sino que les servían a ustedes. Hablaban de las cosas que ahora les han anunciado los que les predicaron el evangelio por medio del Espíritu Santo enviado del cielo.
It was revealed to them that they were not serving themselves but you, when they spoke of the things that have now been told you by those who have preached the gospel to you by the Holy Spirit sent from heaven.
Esa mañana se estaban sirviendo pooris para todos como desayuno, ya que no son picantes.
That morning pooris were being served to everyone for breakfast, as they are not spicy.
Esta era una manera muy fuerte de decir que ellos se estaban SIRVIENDO A SÍ MISMOS.
This was a very strong way of saying that they were SERVING SELF.
Palabra del día
el relleno