וְנָתַתִּ֤י לְךָ֙ אוֹצְר֣וֹת חֹ֔שֶׁךְ וּמַטְמֻנֵ֖י מִסְתָּרִ֑ים לְמַ֣עַן תֵּדַ֗ע כִּֽי־אֲנִ֧י יְהוָ֛ה הַקּוֹרֵ֥א בְשִׁמְךָ֖ אֱלֹהֵ֥י יִשְׂרָאֵֽל׃
And I will give thee the treasures of darkness, and hidden riches of secret places, that thou mayest know that I am the LORD, who call thee by thy name, even the God of Israel.
Read kabbalistic (mystical) interpretation of Isaiah 45:3: and classical mystical sources.