The concept of ¨God's plan¨ is one that Christian Fundamentalists allude to frequently as they feel that a person's life is ¨planned¨ by God; in other words, there is a sense of predestination since God determines when a person will do certain things, events will occur that affect that person's life, and so on. Often such Fundamentalists will refer to a person's dying as ¨his/her time,¨ and they will frequently say, ¨When the good Lord wants to take me, I will be ready....¨ Thus, there is the sense of God's control over one's life and a respectful obedience to the will of God. With this concept of God's direction of one's life, it is, then, wrong for any person to assume the power of control over life and death. In other words, a person cannot ¨play God¨ rightfully and it is wrong for a person to end one's own life.
Jesus taught that death and destruction are the work of ¨the thief"(Satan)
Satan, of course, committed the sin of Pride as he wanted to have power equal to that of God.
Christians are taught to obey the will of God. Among other Christians, Roman Catholics, for instance, believe that one's suffering on earth is God's will, and it also may be a type of ¨purgatory on earth" for which the soul may be rewarded or cleansed of sins committed. Or, it may be perceived as an opportunity for grace and eternal reward. This is somewhat like the persecutions of the martyrs who were made saints for having endured tremendous torture because they would not deny their Christian faith.
Based upon their readings and interpretations of the Bible, many Christians feel that certainly it is not for man to decide when he dies; for, this decision lies solely in the hands of God (His plan). Therefore, by ending one's life, a person disobeys God and commits sin.
(the dailybibleguide link below offers interpretations of scripture that may assist)