The Book of Shir Hashirim is a metaphor for the loving relationship between Hashem and the Jewish people. The verse teaches “the voice of my Beloved… He stands behind the wall, watching through the windows, peering through the cracks.” The word peering - מציץ - is related to the word ציץ - Tzitz. It is also related to the word ניצוץ, meaning a spark – a tiny glimmer of light.
Rabbi Eliezer teaches that from the day the Beis Hamikdash was destroyed, an iron wall separates the Jewish people from their Father in Heaven. Iron represents the forces of negativity. For this reason, iron tools could not be used on the Temple Mount when building the Beis Hamikdash. On the contrary, iron represents the nation of Edom – Rome – who destroyed the Beis Hamikdash.
Hashem loves us with an infinite love. When the Temple stood, this love shone openly and could be felt and seen by everyone. But our sins create a wall of separation that conceals this Divine revelation.
When we have thoughts of Teshuvah, these thoughts create small cracks in the iron wall of separation. We may not have the full revelation, but even in the darkness of Golus, through these cracks we can peer through and receive a small glimmer of this light.
The Tzitz, sitting over the forehead, represents our thoughts of Teshuvah, that break through the concealment; allowing a spark of this light to shine through and enabling us to peer through and catch a glimpse of our Beloved.
Our sages teach that the “voice of my beloved” is the voice of Moshiach, who will come when we do Teshuvah. With enough cracks, the walls of Golus and separation will crumble and we will merit to see the full revelation of our Beloved once more.
~ Based on Or Hatorah Parshas Tetzaveh p1732 onwards
 Shir Hashirm 2:8-9
 Brachos 32b
 Shir Hashirim Rabbah Parsha 2
 Rambam Hilchos Teshuvah 7:5