For my daily quiet time, I've been reading early Christian writings, such as Shepherd of Hermas, Barnabas, and I-II Clement. Their Christianity seems to differ from dispensationalism, particularly the brand I encounter when I read Bullinger and Scofield.
According to the dispensational writings and churches that I've encountered, we're now in the age of grace. Jesus preached to people who were still under a covenant of works, so when he said that God wouldn't forgive them if they didn't forgive others (Matthew 6:14-15), he wasn't establishing a principle that applies to Christians today. For certain dispensationalists, Christians don't forgive others in order to be forgiven by God. Rather, they forgive others because they've already been forgiven by God (see Colossians 3:13). As far as they're concerned, this is the age of grace, which began under the apostle Paul.
Dispensationalists also tend to go with once-saved-always-saved. They point to passages that talk about believers having been sealed with the Holy Spirit unto the day of redemption (Ephesians 1:13; 4:30). For them, a seal is an absolute guarantee that one will enter the good afterlife--no "if"s, "and"s, or "but"s.
But this isn't exactly the view that I encounter in early Christian literature. I'll focus here on I-II Clement, epistles written in the first-second centuries C.E. I'll be quoting the version that appears in The Lost Books of the Bible and the Forgotten Books of Eden.
Regarding forgiveness, let's take a look at I Clement 7:4: "Be ye merciful and ye shall obtain mercy; forgive, and ye shall be forgiven: as ye do, so shall it be done unto you: as ye give, so shall it be given unto you: as ye judge, so shall ye be judged; as ye are kind to others, so shall God be kind to you: with what measure ye mete, with the same shall it be measured to you again."
As far as Clement was concerned, Jesus' principle of forgiving others in order to be forgiven by God still applied, long after Paul had supposedly inaugurated an age of free grace (in the view of dispensationalists). And, unlike certain dispensationalists, Clement deems the Sermon on the Mount to be authoritative for Christians, since he cites it as an authority.
On the seal, let's consider II Clement 3:13, 18: "Thus speaks the prophet concerning those who keep not their seal; Their worm shall not die, and their fire shall not be quenched; and they shall be for a spectacle unto all flesh...This, therefore, is what he saith; keep your bodies pure, and your seal without spot, that ye may receive eternal life."
According to the author of II Clement, the seal of the Christian can indeed be broken, leading to his eternal punishment in hell. That's why he needs to repent. His eternal life is at stake. It's similar to the Catholic belief of "you need to repent of mortal sin before you die."
I don't care for this doctrine, but I don't think I can blithely blow it off, either. People can respond, "Well, Clement isn't the New Testament, and the New Testament is what we follow as Scripture." But if Paul had inaugurated a special dispensation of free grace and eternal security, as dispensationalists maintain, isn't it odd that Christian writers in the second century didn't seem to know about it?