וְ֠הָאֲבָנִים תִּֽהְיֶ֜יןָ עַל־שְׁמֹ֧ת בְּנֵֽי־יִשְׂרָאֵ֛ל שְׁתֵּ֥ים עֶשְׂרֵ֖ה עַל־שְׁמֹתָ֑ם פִּתּוּחֵ֤י חוֹתָם֙ אִ֣ישׁ עַל־שְׁמ֔וֹ תִּֽהְיֶ֕יןָ לִשְׁנֵ֥י עָשָׂ֖ר שָֽׁבֶט׃
And the stones shall be according to the names of the children of Israel, twelve, according to their names; like the engravings of a signet, every one according to his name, they shall be for the twelve tribes.
Read kabbalistic (mystical) interpretation of Exodus 28:21: and classical mystical sources.