אֲבָנִ֤ים שְׁלֵמוֹת֙ תִּבְנֶ֔ה אֶת־מִזְבַּ֖ח יְהוָ֣ה אֱלֹהֶ֑יךָ וְהַעֲלִ֤יתָ עָלָיו֙ עוֹלֹ֔ת לַיהוָ֖ה אֱלֹהֶֽיךָ׃
Thou shalt build the altar of the LORD thy God of unhewn stones; and thou shalt offer burnt-offerings thereon unto the LORD thy God.
Read kabbalistic (mystical) interpretation of Deuteronomy 27:6: and classical mystical sources.