Uhh, redeemedzoomer is a Christian... Public Figure(?) and started this whole movement about retaking the mainline churches and stuff. Something about theological liberalism and all that.
Basically, he's saying that theological liberalism (which is different from political liberalism) is killing off the historic mainline churches. So we, as the newer generation, need to move to whatever mainline church is in our same tradition in order to offset the balance and eventually bring it back to traditional Christianity.
For example, if someone was an evangelical
PCA Presbyterian, he would say to go to a historic
PCUSA church as that is one that needs to return to traditional Christianity.
In my case, I would go from
Independent Christian Church (Campbellite stuff it's confusing) to the
Christian Church [Disciples of Christ]