וְלֹא־יָכֹ֥ל דָּוִ֛יד לָלֶ֥כֶת לְפָנָ֖יו לִדְרֹ֣שׁ אֱלֹהִ֑ים כִּ֣י נִבְעַ֔ת מִפְּנֵ֕י חֶ֖רֶב מַלְאַ֥ךְ יְהוָֽה׃ (ס)
But David could not go before it to inquire of God; for he was terrified because of the sword of the angel of the LORD.
Read kabbalistic (mystical) interpretation of I Chronicles 21:30: and classical mystical sources.