Definition and Nature:
Jealousy, as depicted in the Bible, is a complex emotion that can manifest as a desire for what others possess, whether it be material wealth, relationships, or spiritual gifts. It often stems from a sense of insecurity, fear, or covetousness. The Bible frequently warns against jealousy, highlighting its destructive potential and its roots in human sinfulness.

Biblical Instances:

1. Cain and Abel (Genesis 4:1-16): The first recorded instance of jealousy in the Bible is the account of Cain and Abel. Cain's jealousy over God's favor towards Abel's offering led to the first murder. This narrative illustrates how jealousy can escalate into violence and estrangement from God. "Then the LORD said to Cain, 'Why are you angry, and why has your countenance fallen? If you do what is right, will you not be accepted? But if you refuse to do what is right, sin is crouching at your door; it desires you, but you must master it.'" (Genesis 4:6-7).

2. Joseph and His Brothers (Genesis 37): Joseph's brothers were envious of their father's favoritism and Joseph's dreams, which foretold his future prominence. Their jealousy led them to sell Joseph into slavery. This account demonstrates how jealousy can fracture familial relationships and lead to long-term consequences.

3. Saul and David (1 Samuel 18-19): King Saul's jealousy of David's military success and popularity drove him to multiple attempts on David's life. Saul's jealousy consumed him, leading to his downfall and loss of God's favor. "And Saul was very angry, and this song displeased him. 'They have ascribed to David tens of thousands,' he said, 'but to me they have ascribed only thousands. What more can he have but the kingdom?'" (1 Samuel 18:8).

Teachings and Warnings:

1. Proverbs and Wisdom Literature: The Book of Proverbs frequently warns against jealousy, associating it with rottenness to the bones and a destructive force in relationships. "A tranquil heart is life to the body, but envy rots the bones." (Proverbs 14:30).

2. New Testament Exhortations: The New Testament continues to caution against jealousy, urging believers to live in love and harmony. The Apostle Paul lists jealousy among the "acts of the flesh" and contrasts it with the fruit of the Spirit. "Let us not become conceited, provoking and envying one another." (Galatians 5:26).

3. James on Wisdom and Jealousy: The Epistle of James highlights the contrast between earthly wisdom, characterized by jealousy and selfish ambition, and heavenly wisdom, which is pure and peace-loving. "For where jealousy and selfish ambition exist, there will be disorder and every evil practice." (James 3:16).

Consequences of Jealousy:

1. Spiritual Consequences: Jealousy can lead to a separation from God, as it often results in sinful actions and attitudes. It can hinder spiritual growth and disrupt one's relationship with God and others.

2. Relational Consequences: Jealousy can destroy relationships, leading to mistrust, resentment, and conflict. It can cause divisions within families, communities, and the church.

3. Personal Consequences: On a personal level, jealousy can lead to emotional turmoil, dissatisfaction, and a lack of peace. It can consume an individual, leading to bitterness and a distorted view of self and others.

God's Jealousy:

While human jealousy is often sinful, the Bible also speaks of God's jealousy, which is righteous and holy. God's jealousy is rooted in His desire for His people's undivided devotion and love. It reflects His protective nature and His intolerance of idolatry and unfaithfulness. "For the LORD your God is a consuming fire, a jealous God." (Deuteronomy 4:24).

Conclusion:
The Bible presents jealousy as a powerful and often destructive emotion that can lead to sin and separation from God. Believers are called to guard against jealousy, seeking instead to cultivate contentment, love, and trust in God's provision and plan.