Determining God’s purpose is a complicated issue. I can only briefly describe how a purposeful life is determined, which I believe to be correct according to the Bible. I will be speaking in general terms. Very rarely, it would seem from Scripture, does the Lord call one for his service from the womb. Jeremiah was one and Cyrus was named and called one hundred to one hundred-fifty years before he was born.
Jeremiah 1:5 Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee, and I ordained thee a prophet unto the nations.
Isaiah 44:28 That saith of Cyrus, He is my shepherd, and shall perform all my pleasure: even saying to Jerusalem, Thou shalt be built; and to the temple, Thy foundation shall be laid.
In general, there is no specific plan for an individual’s life. Men come into existence at conception. When two individuals come together to produce an offspring, they create a new DNA sequence as a matter of “time and chance.” DNA contains all the traits of the parents, their parents, and their parents, etc., etc. All the qualities, good as well as all the mutations and corruptions, to the DNA. This is all the product of “time and Chance”. The traits, talents, and abilities you inherit are determined by which genes get turned on or off, and which ones take dominance. DNA is the book that contains all the information about your physical and mental composition. It is the product of “time and chance”, not predestination. It is God’s system of procreation at work, guaranteeing the uniqueness of each individual.
Ecclesiastes 9:11 I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all.
The environment a child is raised in must be added. Are the parents loving or neglectful? Is the child abused or bullied? Was the individual born in an industrialized nation or a third-world country? What type of education was provided? All these things are the result of “time and chance” and make individuals who they are.
Added to this is freewill; biblical freewill is not absolute. Men have freewill of desire, inclination, passion, aspirations, motivations, intentions, likes, dislikes, loves, and hatreds; what we would like or would do if we could avoid the consequences. Take note that an individual can alter or overcome many qualities: physical, mental, or emotional, through a change of heart, which can be influenced by events and various situations. Freewill of action is more restrictive. However, it is man’s desire, good or evil, that the Lord guides and focuses for his purposes.
Taking all this into consideration, God chooses whom he will, whoever fits his needs, for his purposes. God’s calling is predicated upon His requirements, and our desires, education, and skills. Most of us are not called for any specific duty, but are expected to witness and live according to God’s will and laws: love God with all your heart, and love and do unto others as you would have done to you; we are to live godly, righteously, and justly in this present evil world.
As a biblical Christian, this means reading and diligently studying God’s word and preparing yourself to be an effective witness of his saving grace to others. With this foundation, we are free to pursue our desires, keeping within the Scriptures. The Lord will bless and aid you according to the heart’s desire toward him.
Ecclesiastes 11:9 Rejoice, O young man, in thy youth; and let thy heart cheer thee in the days of thy youth, and walk in the ways of thine heart, and in the sight of thine eyes: but know thou, that for all these things God will bring thee into judgment.
As I stated, this is a brief general description. It certainly does not cover every intricate detail of our becoming who we are or God’s dealing with us. It is an opinion based on my studies. I hope it helps.