Are Unconditional Promises Actually...Conditional?

"The opponents of the doctrine of perseverance knew these passages, of course; but they always stress that the 'if,' the conditional, must always be understood in the text, even though it is not found there in so many words. Further, such 'unconditional' texts, they said, had to be understood within the entire conditional context of the Scriptures." (G. C. Berkouwer)