Since the early days of the church, people have tried to deny the Incarnation and still call themselves Christians. The little letter of 2 John is an answer to them and a reaffirmation of the truth about God in the flesh.
Although many Jews did not believe the gospel and many non-Jews did, everyone who calls on the name of the Lord will be saved.
At the Red Sea, the LORD triumphed gloriously, made himself known, and anticipated his greater triumph in the cross and resurrection.
God has always been with his people, in various ways and temporarily in Old Testament times and later and permanently in human flesh.