22:4 What do we learn from this?

We learn from this that (1), God will live visibly among the saints forever in New Jerusalem, ... and they shall see His face (cp Lev 26:11-12; Psa 68:15-18; Isa 33:17; Zech 2:10-11; 8:3; Mt 5:8; 1Jn 3:2; Rev 7:15).

Previously, no one could look upon God and live (cp Ex 33:20-23; Jn 1:18; 1Ti 6:16). And (2) ... His name shall be in their foreheads, means that the redeemed of God are his personal possession (cp Rev 3:12 with Re 7:2-3 and 14:1).