The Month of Cheshvan
The Midrash relates that a similar event occurred with the building of the First Beit HaMikdash, which was completed in the month of Cheshvan. As the verse says, “In the eleventh year (of King Solomon’s reign) in the month of Bul which is the eighth month, the House was finished.” (Cheshvan was called the month of Bul as that’s the month in which the animals are gathered into the house [or stables] due to the rain [בוללים means gathered]. Or because in that month the earth forms into clods due to the rain [בולין means clods]. Or because that is when the מבול /mabul (flood) started.)
During the following 12 months, the people were murmuring and saying that G-d wasn’t happy with the Temple built by King Solomon since he was the son of Batsheva (whom Kind David had married under dubious circumstances). In fact, G-d was delaying the consecration of the Beit HaMikdash until the month of Tishrei, which is when our patriarch Abraham was born. This is why Tishrei is called the יֶרַח הָאֵתָנִים – Month of the Mighty Ones – as Avraham is called אֵיתָן הָאֶזְרָחִִֽי, the mighty one from the East.
The Midrash concludes that G-d is going to repay the month of Cheshvan. This means that the consecration of the Third Beit HaMikdash will take place in the month of Cheshvan. Or that Moshiach will come in the month of Cheshvan.
It had been suggested that this is why king Yeravam established an idolatrous holiday in the month of Cheshvan, knowing the great significance of this month. Others opine that the consecration of the Third Beit HaMikdash in the month of Cheshvan will atone for the sin of Yeravam who established his idolatrous holiday in that month.