This paper is to study and analyze recent important cases held by the Korean Supreme Court. The personal accident insurance has been dealt on the issue of reduction of the claim. The court holds that insurance company can subtract the claim in the ratio of the already suffered disease. However the holding needs to be scrutinized in the aspects of the nature of a personal insurance. This paper also debates the explanation duty of an insurer as applied to insurance coverage disputes. Courts and most scholars have argues for the soul of contract law. Under the traditional contract theory, the assent of both parties to the terms of an agreement is necessary for creation of an enforceable contract. Provisions excluding or limiting coverage, according to the theory, would not be enforceable because of "substantialness". However, it is very difficult to discern the substantial clause and the non-substantial. And so forth, this paper also explorers some the point at issues of insurance law. In this Paper, I enunciate some suggestions of the reasonable theory to our debate about the legal nature of insurance policy.