Why would God institute a system and then declare it weak and useless? It seems counterintuitive, doesn't it? But the author of Hebrews shows us it's not a sign of failure, but of divine progression.
The verse speaks of a "commandment going before" being "set aside" due to its "weakness and unprofitableness." This isn't about God making a mistake. Think of it like building a house. You might start with a basic blueprint (the old commandment) that gets you started. But as you learn more and have better tools and materials (Christ's priesthood), you create a more detailed, robust plan that builds something far greater and more enduring.
The "commandment" here refers specifically to the Levitical system – the rules and regulations that established the earthly priesthood. It served its purpose for a time, like a schoolmaster guiding people. However, it couldn't ultimately bring people into true, intimate fellowship with God. It was "weak" because it couldn't perfectly atone for sin or grant righteousness, and "unprofitable" in the ultimate sense of salvation and drawing near to God. This isn't a condemnation of the Law, but an acknowledgment that it was a temporary, preparatory measure.