These were another twelve stones (cf. v. 3), signifying the twelve tribes of Israel in their old life and in their old nature. Joshua erected these twelve stones in the middle of the Jordan where the Ark was, signifying that the Lord wanted Israel in their old nature to remain under the death water of the Jordan. This typifies that the old man of the believers should remain in the death of Christ (Rom. 6:6; Gal. 2:20; Phil. 3:10).
The two sets of twelve stones signify that our old man has been buried and our resurrected new man is living and working with the Triune God as one. This corresponds with the revelation in Eph. 2:1, 4-6, 10, 15.