וַיֵּ֙דַע֙ כָּל־יִשְׂרָאֵ֔ל מִדָּ֖ן וְעַד־בְּאֵ֣ר שָׁ֑בַע כִּ֚י נֶאֱמָ֣ן שְׁמוּאֵ֔ל לְנָבִ֖יא לַיהוָֽה׃
And all Israel from Dan even to Beer-sheba knew that Samuel was established to be a prophet of the LORD.
Read Kabbalistic (mystical) interpretations of I Samuel 3:20: Zohar and classical Jewish mystical sources, free online.