וְיָדַעְתָּ֖ עִם־לְבָבֶ֑ךָ כִּ֗י כַּאֲשֶׁ֨ר יְיַסֵּ֥ר אִישׁ֙ אֶת־בְּנ֔וֹ יְהוָ֥ה אֱלֹהֶ֖יךָ מְיַסְּרֶֽךָּ׃
And thou shalt consider in thy heart, that, as a man chasteneth his son, so the LORD thy God chasteneth thee.
Read kabbalistic (mystical) interpretation of Deuteronomy 8:5: and classical mystical sources.