There is a lot of backing an forthing on this topic. Best is to make it clear in a decisive way, then follow the logic. Reduction potential is a measure of how much something wants to undergo reduction (losing O, gaining electrons, going down in oxidation state). Nonmetals reduce naturally and metals oxidize. The value of the reduction potential is more positive if the reduction is thermodynamically favorable. if a reduction potential is negative, that means that the reaction wants to go backwards - oxidation takes place.
Here's where things get out of hand... a reducing agent is something that gets oxidized: Sodium is a strong reducing agent as it will force electrons onto just about anything because it oxidizes so easily. Now, we can understand why a large negative reduction potential (something that strongly wants to oxidize) is a good reducing agent(something that reduces other things by oxidizing).
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