כִּ֛י אִם־מָאֵ֥ן אַתָּ֖ה לְשַׁלֵּ֣חַ אֶת־עַמִּ֑י הִנְנִ֨י מֵבִ֥יא מָחָ֛ר אַרְבֶּ֖ה בִּגְבֻלֶֽךָ׃
Else, if thou refuse to let My people go, behold, to-morrow will I bring locusts into thy border;
Read kabbalistic (mystical) interpretation of Exodus 10:4: and classical mystical sources.