One of the more compelling scriptural evidences for the doctrine of universal salvation is found in Paul's letter to the Romans, in the fifth chapter. Following a brief discussion of the different effects of Adam and Christ on humanity, Paul terminates the section with the following affirmations:
Therefore just as one man’s trespass led to condemnation for all, so one man’s act of righteousness leads to justification and life for all. For just as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous (Rom 5.18-9).
The idea here seems obvious enough: Adam's effects were universally bad; Christ's effects will be universally good.
Some persons try to escape the conclusion by understanding "all" as "Jews and Gentiles alike," without insisting that it includes every individual Jew and Gentile. This line of thought is not plausible, to my mind, and I will try to demonstrate why.
It seems to me that the critical interpretive point for understanding the universalized language in Rom 5.18-9 is found at 3.9, where Paul summarizes his case for universal sinfulness: We have already charged that all, both Jews and Greeks, are under the power of sin. The Greek text here is as follows: Ἰουδαίους τε καὶ Ἕλληνας πάντας, Jews and Gentiles alike all. Nobody supposes that Paul envisions some possible exceptions to the argument for universal sinfulness in these opening chapters of the letter to the Romans: it is not as if there might have been a Jew or Gentile here and there who had never sinned and was not under the power of sin, and consequently had no need of Christ's salvation. Paul's language here is universal in the true sense: it applies to each and every person.
Now this sense of "all" is clearly carried over into the subsequent discussions, since it is precisely this problem of universal sinfulness that Paul's gospel addresses. For instance, what he says in Rom 3.23-4 clearly must be applied distributively to all human persons: all have sinned and lack the glory of God; they are now justified by his grace as a gift. Here too Paul affirms universal salvation as God's gift through Christ. There is no reason to delimit the domain of "all" here when the pivotal verse for the entire discussion clearly implies a universal reading.
All the same points may be made mutatis mutandis in the case of Rom 5.18-9. Paul envisions Adam's sinfulness to have extended to all human persons as evidenced by their death (5.12). Importantly Paul emphasizes that Christ's righteousness has a greater efficacy than Adam's sinfulness numerous times (v. 15-7). He says that the free gift is not like the trespass (v. 15), and accents that much more surely the gift of God will take effect and destroy the works of Adam (cf. 1 John 3.8). He does mention those who receive the abundance of grace in v. 17, but this passage is not as significant as so often supposed. His point throughout this is all is that salvation was something given by God, not something accomplished by man. Death was brought about because of the one man's trespass (v. 17); it is something humanity accomplished for itself, whereas salvation is a free gift (v. 15). Beyond this, Paul says receive, not accept -- his point is that humanity is a passive recipient of God's gift of salvation. In any case the analogy between Adam and Christ, along with the affirmed superiority of Christ's work, clearly demands that even the language of acceptance, if it is insisted upon, be universalized -- Christ's work is greater than Adam's, so that all will eventually accept it and be saved.
This attempted evasion of the universalist argument of Rom 5.18-9 is therefore a failure.