בָּנִ֛ים אֲשֶׁר־יִוָּלְד֥וּ לָהֶ֖ם דּ֣וֹר שְׁלִישִׁ֑י יָבֹ֥א לָהֶ֖ם בִּקְהַ֥ל יְהוָֽה׃ (ס)
The children of the third generation that are born unto them may enter into the assembly of the LORD.
Read kabbalistic (mystical) interpretation of Deuteronomy 23:9: and classical mystical sources.