It is true that the nature of our present existence, even as given by God, makes some effort on our parts necessary in order to attain some level of and quality in life. We do eat by the "sweat of our brows" after all. But it seems to me that the necessity of earning at that level tends to makes us self-centered--we tend to think of living in terms of my effort, my reward, my ambitions, my desires. In the unending swirl of all that self-centeredness, one can forget (or even never awaken to) the fact that our very life, our very breath, is a gift from God.
According to the record of scripture, we only need to work so in order to get because of a curse imposed because of sin. Sin is in the world, sin is in us. If it was not for sin, however, we would not have death over our heads and we would not have to sweat to get our bread. Take sin out of the equation and we would have freely what God freely, liberally, gives us and it would be crystal clear that all was a gift from God.
This can be difficult for us to embrace. It is almost as if our sweating for our bread, the toil of scratching out a living separated from God all the while dying, plays a trick on us. Even if we happen to be aware of God's part in the big picture, we tend to project the concept of earning upon any blessing we could get from God. We think we have to earn whatever blessing we may be seeking from God, even as we have to earn to eat.
Even if we ask God for blessing we do so as earners, not as gift recipients. We seek his favor by making promises to him or by citing our rewardable behaviors. We try to find some valid reason for us to receive the reward we seek. Even if we haven't earned such a blessing in the past, we assure God we will do so in the future should he make that blessing ours.
All such boasting is antithetical to the purposes of God, and let's be clear, what that is, is boasting. Even more than that, it is living by the principles of the present darkness, it is living by sight. Sight, in effect, says "give me what I deserve", but faith says "give me what you're willing to". Perhaps the greatest threshold faith must cross is getting over the boastful notions of humankind, borne of the reality of this present existence, that can only see life through the prism of getting what you've worked to gain.