וַיְדַבֵּ֥ר מֹשֶׁ֛ה אֶל־בְּנֵ֥י יִשְׂרָאֵ֖ל לַעֲשֹׂ֥ת הַפָּֽסַח׃
And Moses spoke unto the children of Israel, that they should keep the passover.
Read Kabbalistic (mystical) interpretations of Numbers 9:4: Zohar and classical Jewish mystical sources, free online.