进一步说明什么样的人才是有资格执政。每个人都要经过教育、考验并从中获得能力认证的人。这点出了民主是要起点平等，过程平等，以及结果平等，一切只看能力。过程中的考验成了关键：如何判定人过不过关。

Every man shall have an equal chance to make himself fit for the complex tasks of administration; but only those who have proved their mettle (or, in our myth, their metal), and have emerged from all tests with the insignia of skill, shall be eligible to rule.
每个人应当享有均等的机会让自己具备胜任复杂行政事务的能力；但是只有那些证明了自身能力（或者按我们流行说法，指的是他们的金属属性），并通过所有考验且获得认证的人，才有资格执政。

细节解析

1、make oneself fit for ：让自己具备胜任……的能力
Without doubt he would leave Middlemarch, go to town, and make himself fit for celebrity by "eating his dinners".毫无疑问，他会离开米德尔马城进城去，让自己成为名人。《米德尔马契》
2、mettle：strength of spirit; ability to continue despite difficulties应对困境的勇气，才能，气魄
The army in butternut were now seasoned fighters, their generals had proven their mettle, and everyone knew that when the campaign reopened in the spring, the Yankees would be crushed for good and all.那些穿灰制服的军队已成为久经沙场的队伍，他们的将军已屡奇功。人人都知道，只要春季战役一打响，北方佬将被永远彻底地击溃了。《飘》
3、insignia：a badge or sign which shows that a person is a member of a particular group or has a particular rank（常指军队的）徽章，标志，识别符号
He's dressed in his uniform, sober black with the rows of insignia and decorations.他穿着制服，朴素的黑色，带胡一排排的徽章和装饰品。《使书的故事》

所在段落

The Story of Philosophy《哲学的故事》第1章Plato第7节VI. The Political Solution第1段第3句：

Automatically — without any hypocrisy of voting. Democracy means perfect equality of opportunity, especially in education; not the rotation of every Tom, Dick and Harry in public office. Every man shall have an equal chance to make himself fit for the complex tasks of administration; but only those who have proved their mettle (or, in our myth, their metal), and have emerged from all tests with the insignia of skill, shall be eligible to rule. Public officials shall be chosen not by votes, not by secret cliques pulling the unseen wires of democratic pretense, but by their own ability as demonstrated in the fundamental democracy of an equal race. Nor shall any man hold office without specific training, nor hold high office till he has first filled a lower office well(Gorgias, 514-5).
浙江大学译本： 每个人应当享有均等的机会去培养和锻炼自身的能力，以适应管理国家的复杂任务；但只有那些成功证实了自己的气质（或者如我们的神话中说的，他们所属的金属质地）、以卓越实力突破所有测试的人才能成为统治者。

上句见：Day432