Man has done nothing to merit a blessing. Rather, God speaks it out of his own purpose and desire. Like the primal word of creation, the initial blessing arises from God's own purpose, and it produces life. So man receives this creative word of blessing at the outset and it becomes part of his ideal spiritual nature, defining his entire relationship with his Creator. The original blessing includes the command to subdue the earth.
Work is part of the blessing.
The Hebrew root for tend is avad, from which comes the word avodah, meaning labor, or even bondage. Later in the Torah, this same word also comes to mean worship, as in avodat mishkan, the service or worship of the Tabernacle. Avodah becomes the general term in Hebrew for worship. Perhaps worship and work are not so far apart in the mind of God. The root verb here is shamar, which means to guard.