You and your spouse may disagree on something, and you may think you are right and your spouse is wrong. You may feel so strongly about being right that you are not prepared to give in and settle, but rather would prefer someone tell you if you are right or wrong.
A trial has the purpose of figuring who is right and who is wrong, as the judge will hear from you and any witnesses you think have important things to add, and will also hear from your spouse and witnesses your spouse thinks will have important things to add, and then the judge makes a decision.