Leviticus 26:45 is designed to recall the events of the Mosaic covenant which the Lord had established with the nation at Mount Sinai. This event would still have been fresh in the minds of the original hearers. For subsequent generations, especially those who may be in exile, this event would be in the past.
45 Je me souviendrai en leur faveur de l'ancienne alliance, par laquelle je les ai fait sortir du pays d'Egypte, aux yeux des nations, pour être leur Dieu. Je suis l'Eternel.