This is the 10545th most frequent Russian word.
включался
"Включался" means "was turning on" or "was being activated."
The verb 'включался' here is reflexive and indicates an action of beginning operation or turning on something.
Радио самопроизвольно включался среди ночи.
The radio would spontaneously turn on in the middle of the night.
In this case, 'включался' metaphorically means 'became involved' or 'joined' in the discussion.
Он всегда включался в обсуждение темы активно.
He always actively participated in the discussion of the subject.
The use of 'включался' here refers to the light being turned on and starting to emit light.