Mosiah 21:31

yea, they did mourn for their departure, for they knew not whither they had fled. Now they would have gladly joined with them, for they themselves had entered into a covenant with God, to serve him, and keep his commandments.

They were sad that they had left. They didn’t know where they had gone. They would have gladly joined them. They themselves had made a promise with God to serve him and keep his commandments.

They mourned their departure because they didn’t know where they’d gone. They would have gladly joined them, because they too had made a covenant with God to serve him and keep his commandments.