The concept of הסתר פנים is mentioned in פרשת וילך. This refers to Hashem hiding His face, so to speak. We know that Hashem is always there running the world, but there are times when He is hidden. This is הסתר פנים.
Rabbi Soloveitchik wrote that the Holocaust was a period of הסתר פנים for the Jewish people. The State of Israel represented an end to Hester Panim.
The Rav explains this concept further. Hashem brings justice to the world either by מידת הדין, strict judgement, or Hester Panim. The latter is worse.
A child is able to handle a reprimand or punishment. However, rejection is unbearable. When a parent refuses to speak to his child and wants nothing to do with him, the child experiences a horrible void and pain.
The same is true of עם ישראל during periods of such rejection from G-d. Thankfully, when we now call out to Him, Hashem hears our prayers. The Shechina, Divine Presence, has returned to Israel along with 6,600,000 Jews. No more Hester Panim. The גאולה is imminent! Shabbat Shalom