Amplified Bible (AMP)
17 When they enter the gates of the inner court, they shall be clothed in linen garments; no wool shall be on them while they minister at the gates of the inner court and within the temple.
18 They shall have linen turbans on their heads and linen breeches upon their loins; they shall not gird themselves with anything that causes [them to] sweat.
I used to joke about exercising, "The eleventh command says, 'Thou shalt not sweat.'" Later, I found that maintaining a healthy body requires consistent sweating exercise. This type of exercise enhances the body's circulation, which carries immune systems cells, nutrients and oxygen to all the cells in our body. Exercise, sweating exercise is good, very good.
But sweating while serving God isn't spiritually healthy. The Old Testament priests were commanded to "not gird themselves with anything that causes [them to] sweat." Physically, sweat mixed with skin bacteria causes us to stink. God didn't want stinky priests. :) But I believe there is a deeper spiritual aspect to this command. I think sweating is representative of striving.
God provides us with grace. It's grace that empowers us to serve Him, His power in and through us, not our own strength of mind or body. When we strive, it's like we are saying to the Lord, "I don't need Your help. I'm good. I just need to work harder or think longer, then I will be successful in completing the destiny You have set for me. Striving is sweating (hard work) and that is not the "yoke" the Lord has given us.
For My yoke is wholesome (useful, good—not harsh, hard, sharp, or pressing, but comfortable, gracious, and pleasant), and My burden is light and easy to be borne.
If you feel like serving God is burdensome, if you catch yourself striving to complete your destiny, remember, what God has commanded, "they shall not gird themselves with anything that causes [them to] sweat." Grace empowers us to serve Him, no sweat!