The first lesson at Great Vespers (Genesis 28:10-17) describes Jacob’s dream of a ladder reaching from earth to heaven, and the angels ascending and descending upon it. The second lesson (Ezekiel 43:27-44:4) speaks of the gate of the sanctuary which faces east. God enters through this gate, which is shut so that no one else can enter by it. The third reading (Proverbs 9:1-11) talks about the house that Wisdom has built.

These readings are interpreted as prefiguring the Mother of God.

Source:  www.oca.org