Please remember man is very stubburn and perhaps no method will be able to convince everyone. God appeared on Mt. Sinai in the Exodus for 40 days. At first the people were in shock and awe. Not too long after they made themselves a gold calf and to replace Yahweh. Only forty days and the congregation went astray in rebellion.
The arriving at "the oneness of the faith" is a process. All who are saved will arrive eventually at this oneness. All may not arrive at the same time.
"Until we all arrive at the oneness of the faith and of the full knowledge of the Son of God, at a full-grown man, at the measure of the stature of the fillness of Christ.
That we may be no longer little children tossed by wves and carried about by every wind of teaching inthe sleight of men, in craftiness with a veiew to a system of error,
But holding to truth in love, we may grow up into Him in allt hings, who is the Head, Christ..." (Eph. 4:13-15)
1.) Paul discribes a process of gradually arriving.
2.) Paul includes himself in this process - "Until WE ALL arrive at the oneness ..."
3.) The implication is that all the believers are arriving but not necessarily that all arrive at the same time.
4.) Immature children are easily tossed by teachings of men.
5.) The mature should hold to the truth in LOVE.. Not just correct doctrine is vital but love.
6.) The destination if a full grown corporate representation of Christ - the measure of the stature of the fulness of Christ.
We should not be discouraged as Christians. Some are arriving and all will eventually arrive.
If some were not arriving at maturity we would probably not have the exhortation to imitate those who are "inheriting the promises":
"That you be not sluggish, but imitators of those who through faith and long-suffering are inheriting the promises." (Heb. 6:11)
It seems that some were inheriting the promises of oneness and unity in the Body regardless of the fact there were still divisions among Christians on earth.
Christ Himself assures us that the corporate body of His people must be "perfected" and perfection is not instantaneous. It is a process:
"I in them, and You in Me, that they may be PERFECTED into one, that the world may kinow that You have sent Me and have loved them even as You have loved Me." (John 17:23 my emphasis)
Christ's great prayer for the oneness of His people is a matter of them being in the PROCESS of being PERFECTED into one.
We need not dispair and bemoan that no such oneness exists. Rather we should expect that SOME are arriving at the oneness. And we should seek to be imitators of those who through faith and long-suffering are inheriting the promised oneness.
Waiting for new methods could be misleading.