This is a concise and clear statement. There's not much to paraphrase without losing meaning or adding unnecessary words. Here are a few minor variations, but they are very similar:
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Option 1 (Focus on speed): Our top priority: Fast courier service.
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Option 2 (More formal): Courier services are our primary offering.
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Option 3 (Slightly more descriptive): We specialize in providing courier services.
None of these significantly alter the original meaning. The best option depends on the surrounding context.