The answer is: Cain's fruit of the ground

Genesis 4:3-5 - Cain presented the first offering to God from his crops, contrasting with Abel’s offering of a lamb. This act signifies varying motivations and acceptance in worship. Notably, Abel's offering was favoured, hinting at deeper theological themes of sacrifice and faith seen later in Christ’s perfect atonement (Hebrews 11:4).

In Genesis 4:3-5, we witness the debut of offerings in the biblical narrative — a fascinating moment brimming with lessons about intentions and priorities in worship. Cain carted forth what he cultivated from the land, demonstrating hard work and commitment; yet his offering was rejected by the Lord. Abel’s pastoral gift of a lamb thrived more favorably, igniting further contemplation on the essence of giving.

One can draw parallels to later events. Much like Abel’s willingness to offer a lamb, the concept of sacrificial offerings resonates throughout the Bible, ultimately paving the way to the New Testament narrative of sacrifice embodied in Jesus. The connection between Cain and Abel sparks interest as well — the name Abel itself means “vanity” or "breath," hinting at the transient nature of life and the soul’s positioning before the divine potentially begging the question of spiritual depth in our endeavors.

Fun fact: This encounter not only starts the discourse on worship offerings but also introduces sibling rivalry, leading to the first murder noted in the Bible. This striking dynamic reveals how jealousy and acceptance can alter relationships, exemplifying broader lessons regarding community and individual responsibility before the unseen Forces.

As worship practices have evolved, so too has our understanding of sacrifice, challenging all to reflect upon their motives and the heart behind their offerings in life — a poignant wonder that since that early offering, the divine acceptance continues to require more than mere surface acts.