I tried to skim through this thread thus far, and I'm sure I've missed many points that have been discussed, and I really hope I'm not hijacking to interject here.
I was raised to think of a dispensation as a "when" thing. After reading my Bible independently, seriously, and with abandon belief, I see how that misconception of the term leads to innumerable unbeliefs. I hope you'll tolerate this post of me sharing what I've learned of dispensation from scripture and its Author and absolutely no other earthly person:
Jesus used the term dispensation when he told the parable of the unjust steward who was about to lose his dispensation (job, responsibilities, stewardship). The apostle Paul speaks of the dispensation of the fulness of times (again: job, responsibilities, stewardship) where God dispenses an assignment (dispensation) to Jesus to
"gather together in one all things in Christ, both which are in heaven, and which are on earth".
As you know, the epistles of Ephesians and Colossians parallel each other, so this same assignment (job, responsibilities, stewardship) of God to Jesus is mentioned in Colossians 1:19-20 (hyperlink not intended)
"For it pleased the Father that in him should all fulness dwell; And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven."
So God will have Jesus carry out that end-time dispensation (assignment, job, responsibility, stewardship) of "gather together in one all things" or "reconcile all things".
Other New Testament uses of the term dispensation are I Cor 9:16-17, Eph 3:2 and Col 1:25 every single one of which are specifically speaking of Paul's dispensation (assignment, job, responsibility, stewardship) from God to deliver the Gospel to the readers of those epistles.
In other words, "dispensation" has nothing whatsoever to do with "when". It is the assigning by one in authority of a task to one under that authority to perform for them.
The correct alternate way of viewing God's dealing with mankind over history is this found in Deut 29:29:
"The secret things belong unto the Lord our God: but those things which are revealed belong unto us and to our children for ever", [not to be discarded at the end of some made-up "dispensation".]
The most difficult block for most Christians to understanding this radically different concept of dispensation is that they have been led to think in terms of the Law of Moses as a supposed means of salvation gave way to salvation by the Cross, so thereby was a new dispensation ushered in. That notion is falsified by two witnesses against it: Paul states emphatically that the Law could never have given salvation because salvation had always been and still is by grace through faith. The second witness against that notion is the very clear and unambiguous declaration that obedience to the Law of Moses served the purpose of, not personal salvation, but distinguishing the nation of Israel from all other nations:
Ex 19:5 and elsewhere
"Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people"
Does all this resonate with you?