Ariadnne,
The answer to your question will depend on the largely theological paradigm in which you work. Based on the way you framed the question, I imagine that you are approaching this from a Catholic or Orthodox perspective—though it is possible to address this from a multiplicity of Protestant views as well. I will default to the latter two and save Protestantism for a different time.
In short, holy orders are important if you see the church as having a ministerial priesthood that is distinct from the priesthood of all believers. If valid sacraments require the bestowal of authority to perform them, then it will be important to have some way of bestowing this authority to those presiding over them. Holy orders offer this means of doing so.
I hope this helps. If you wish to discuss this question (or others like it) more, please feel free to reach out.
