The text is about AD 70, which is the destruction of Jerusalem and the temple. The disciples question Jesus about this and wanted to know the time when this would happen.
In Mark 13:35 there is a phrase that is relevant to us today. Be Alert! These words are used to warn the church and the individual Christian, to be wide awake in this world. For His coming in the present and also in the future when he will return to take us home.