The Scofield Bible Commentary, by Cyrus Ingerson Scofield, [1917], at sacred-texts.com
Joshua Chapter 4
The two memorials
The two memorials. The twelve stones taken out of Jordan and erected by Joshua in Gilgal, and the twelve stones left in Jordan to be overwhelmed by its waters, are memorials marking the distinction between Christ's death under judgment in the believer's place (Psa 42:7); (Psa 88:7); (Joh 12:31-33) and the believer's perfect deliverance from judgment. The stones in Jordan stand, typically, for (Psa 22:1-8).
first month
That is, April.