Walking in the Spirit
If you fill a bucket with a gallon of water and carry it on your head it quickly grows heavy and tiresome. In contrast, if you swim underwater you have many gallons of water on top of your head and the weight is not really burdensome. The environement that you are in alters your response to the burden. When you are in an environment of air, water is hard to carry. When you are in the environment of water it is much easier. Walking in the Spirit has the same effect. If you are in the environment of the flesh, then God's command can be burdensome and heavy. If you are in the environment of the Spirit they are much easier. His yoke is easy and His load is light.