There is no doubt that the Gospel of Christ was preached to Abraham and to our forefathers by the Prophets starting from Prophet Enoch, the seventh from Adam and later on through Christ then ministered by the Apostles with the help of the holy spirit.
Gal 3:8 And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, [saying], In thee shall all nations be blessed.
Heb 1:1 God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets,
Heb 8:8 For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
And this is the new covenant made by God with the house of Israel and with the house of Judah not in tables of stone, but in fleshy tables of the heart.
2 Cor 3:3 [Forasmuch as ye are] manifestly declared to be the epistle of Christ ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart.
Ezek 11:19 And I will give them one heart, and I will put a new spirit within you; and I will take the stony heart out of their flesh, and will give them an heart of flesh:
But the people who don’t understand and can’t or haven’t read, God has his own way of them knowing the Gospel.
Rom 2:12 For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by the law;
Rom 2:13 (For not the hearers of the law [are] just before God, but the doers of the law shall be justified.
Rom 2:14 For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves:
Rom 2:15 Which shew the work of the law written in their hearts, their conscience also bearing witness, and [their] thoughts the mean while accusing or else excusing one another;)
This is because, the laws put by God into their mind and written into their hearts are working into action.
Heb 8:10 For this [is] the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
Jer 31:33 But this [shall be] the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
Christ after he rose up from the dead, descended and preached the Gospel to the spirits in prison held captive at the lower parts of the earth.
Eph 4:9 (Now that he ascended, what is it but that he also descended first into the lower parts of the earth?
1 Pet 3:19 By which also he went and preached unto the spirits in prison;
1 Pet 3:20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.
1 Pet 4:6 For, for this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit.
Eph 4:8 Wherefore he saith, When he ascended up on high, he led captivity captive, and gave gifts unto men.
Those are the spirits in prison at the time of Noah but how about those at the time of Lot – when Sodom & Gomorrah was destroyed, Are they not included in the preaching of Christ? There is no other “lower parts of the earth” mentioned in the Bible where the spirits are held captive, so we have reason to believe that they are also included.
Accordingly Saint Paul said, the Gospel is heard and preached to every creature which is under heaven.
Col 1:23 If ye continue in the faith grounded and settled, and [be] not moved away from the hope of the gospel, which ye have heard, [and] which was preached to every creature which is under heaven; whereof I Paul am made a minister;
Gal 1:11 But I certify you, brethren, that the gospel which was preached by me is not according to man.
Gal 1:12 For I neither received it from man, neither was I taught it, but by the revelation of Jesus Christ.
The basis of God’s judgment is the Gospel. It is but logical to say that truly, the Gospel is preached to all men from the beginning of its creation.
Rom 2:16 In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.
Can anyone then on the day of judgment invoke that he was not informed?
Rom 1:20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: