(Which he had promised afore by his prophets in the holy scriptures,)
There are no significant textual transmission issues in this verse.
1. This verse is Paul's claim to be in harmony with Old Testament revelation.
2. The words indicate that God made certain, specific, written "promises" in past time that fundamentally identify His "Gospel".
3. The words also indicate that God has a typical "method" of revelation: "prophets", and, then, "the writings of such men".
4. The words indicate that the "writings" of these "prophets" are "holy" (indicating a clear basis for elevating them above the other writings of men).
1. It is impossible for men to conceive of a "promise" that can be held to be the consequence of "integrity" unless it is "kept".
2. It is also impossible for men to conceive of anyone's ability to "keep" a promise unless they have some dominion over their circumstances.
3. It becomes rather apparent, then, that, unless it can be established that men have dominion over their circumstances, men have no business making "promises".
4. And, it also becomes apparent that God must, by making promises, intend to control the events of history to the degree that His verbal commitments will take place as He said.
a. There are actually two ways God could "make promises about the future" so that they would be "kept".
1) By using omniscience as a kind of "time-telescope", He could simply "look down the progress of time" and see "what" was to come to pass and then promise "that".
2) By getting personally involved in the events of time, He could "do" whatever needed to be done to bring whatever He had "before promised" to pass.
b. In the above scenarios, God is not a "keeper" of His promises as an omniscient observer Who only promises what He sees; whatever is in place to move history to what He sees is actually the performer of the promise, God is simply the "before-the-fact" announcer. He is only a "keeper" of His promises if He actually gets involved in "doing" so that what He promised is the "work of His doing".
5. The question that is raised by "the apparent control of God" is "how much of history is controlled?"
a. At this point, some degree of "theological danger" exists.
1) If men attribute "mechanism" to the issue of the control of history, fatalism is the inevitable result. This is a "deistic" view of history in which "God" set up the first "causes" and all "results" spring from them in a tight "this cause generates this effect, which in turn becomes the cause for the next result in the on-going sequence" kind of order. In a mechanistic universe, there are no "miracles" (insertions of new "causes" by God at points along the way) allowed. If God's creation is so tightly tied to cause/effect that "nothing" is permitted that has the characteristic of being a "first effect, caused by divine intervention", then the universe is mechanistic and fatalistic. Since the biblical record is full of divine interventions, it should be obvious that His creation is not "mechanistic", nor it is to be understood on the basis of omniscience.
2) However, if there are "results" that can occur from more than one "cause", then 'general dominion' is all that is necessary to bring history to its destiny. The question here is whether there is any "slop in the gears" to permit the exercise of "non-mechanistic volition". Those who say there is not, operate under the line of despair and face the judgment of God for rejecting Him and His promises because "they cannot apply (to me)."
3) On the other hand, if men attribute "unbridled free will" to the issue of the control of history, "openness" is the inevitable result and nothing can be "promised". Those who say that God will not violate a person's "free will" operate above the line of conceit and face the judgment of God for rejecting Him and His Words because "I can make my own decisions, thank you!".
b. Biblically, all that is necessary for men to "believe" is what God has "said", not what He has not said. In other words, God doesn't have to personally dominate the vibration of every atom to the degree that nothing can be "decided" by other persons within His creation. All He has to do is dominate what has to be dominated so that, what He has said will be, comes to be.
c. These are the issues that bring out the debate between "Calvinism" and "Arminianism": the questions are two: 1) how specific is divine control?, and 2) how do we know? The answers are given in "the holy writings".
6. Perhaps the biggest "bug-a-boo" in this entire issue of God's "aforepromised" Gospel is this: to whom were the promises made?
a. When we have a specific "promise-text" in mind, it is not difficult to find, in that text, the identity of the recipient of the promise. For a clear example, consider the covenants. When God promised Noah that He would never again flood the earth as He did in his day, it is not hard to see that the promise was to Noah. When God promised Abraham a "seed", it is not hard to see that Abraham should have expected a "seed". When God promised David "an enduring house", David is the recipient of "an enduring house".
b. The problem occurs when the "promise-text" is "open" -- i.e. the recipients of the promise(s) are not identified specifically. Enter, at this point, the "whosoever will" texts that arise because the "promise" is made, not to specific individuals, but in "broadcast form" [God commandeth all men everywhere to repent...Christ died for "our" sins (as a public pronouncement without regard for who might "hear" it)...have they not all heard? indeed they have!...etc.]
1) The issue here is: how do I decide that the promise is to me ? In other words, "how do I become a believer?"
2) Herein stands the legitimacy of the judgment of God: if the "promise" is "open" and "I" do not embrace it as "for me", what is the cause of that? There are always reasons.
a) I will reject it if I have no "faith" that its content comes from "the God". This is the problem of identifying the Author and Content of true divine revelation. It is not an insoluble problem. Once this issue has been resolved, there are other reasons I may reject "His promises"...
i. I may refuse to embrace it for conceit reasons [who needs the promise?]...
ii. I may refuse to embrace it for despair reasons [He cannot have meant me]...
iii. I may refuse it for obstinance reasons [I will NOT have Him rule over me]. [Does not the judgment of God rightly fall upon those who reject His promises when they know that they are His promises?]
b) I will reject it if I have no "interest" in its content. This is the "love" issue. If I do not value life under God's dominion, I will have no interest in "believing a promise that is designed to bring me under His dominion".
7. The next big issue involves why God makes His promise known through His prophets and their writings: why this 'bottleneck'?
a. If God can make His promise known to any man (prophet), why does He not make it known to every man (are all prophets?)?
b. In like vein, if God can produce "holy writings" through any man, why does He not simply produce the content of that information for the consideration of every man?
1) Paul seems to respond to this question in Romans 1 and 10 where he declares that "all" "know" and "have heard".
2) In both texts, he 'generalizes' what is known and heard to a very fundamental level that does not include much 'specific' information. God "is" and "has spoken" and all men know it and that makes them "responsible". That they have no specific details at their disposal is of little to no consequence: why would anyone go to any length at all to extrapolate details to a non-audience? If men do not want to know, why tell them?
c. Prophets and writings are only for greater "depth" of understanding: thus, the number who have access to the prophets and their writings (i.e. the breadth of exposure to the greater explication of the basic message) is limited to some degree by desire alone. If you don't want it, you won't get it no matter how "surrounded" you are, and if you want it, you will get it no matter how "isolated" you are!
8. A related issue in this text is Paul's declaration that his message is in absolute harmony with the written message as given by God's recognized prophets.
a. Obviously, even if a person wants to know the truth from the God Who provides through the bottleneck, there must be some way to "tell" if the "truth" being delivered is really from the God of the bottleneck.
b. Paul's method of addressing this question is to claim: see if what I tell you isn't already established because God has already established it in writings that already have the divine stamp upon them.
1) Obviously, those who wish to compare the message to the aforepromised message have to have the writings of both messengers in hand.
2) Just as obviously, no one is going to "compare" unless he already acquiesces to the notion that the Truth is internally consistent and already a "given".