Even God Himself testifies against the notion that He has written off all other churches. Consider this reality... God is pouring out His own Spirit in nearly every denomination of Christianity. Even today 36% of Catholics have experienced the "charismatic blessing" (baptism of the Holy Ghost with speaking in tongues). You see, while they are still bound with much tradition and errant theological notions... God is moving. I've seen entire Baptist churches swept away in the Holy Ghost with masses speaking in other tongues. Even a local Episcopal church pastored by a skeptical female bishop has opened up "Spirit Filled" services for Episcopls who have received the baptism of the Holy Ghost.
The Spirit of God testifies against the notion that only the UPCI or ALJC have a monopoly on Salvation. The Kingdom of God is so much greater than our denominational traditions, standards, and methods:
Romans 14:17
For the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost.
It's not a matter of what you and I THINK. What matters is what God is ACTUALLY DOING. LOL