This is the 299th most frequent Armenian word.
որովհետև
"Because."
Here, "որովհետև" is used to indicate the reason for being late.
Ես ուշացա, որովհետև մեքենաս չաշխատեց։
I was late because my car didn't work.
In this sentence, "որովհետև" explains the cause of him not attending the class.
Նա չէր մասնակցել դասին, որովհետև հիվանդ էր։
He didn't attend the class because he was ill.
The usage of "որովհետև" in this case provides the reason for not being able to go for a walk.