John 6:27 Labour not for the meat which perisheth, but for that meat which endureth unto everlasting life, which the Son of man shall give unto you: for Him hath God the Father sealed. 

The book of Hebrews tells us about the labour for entrance into rest. This is where faith is born in our heart unto salvation in any situation. Hebrews 4:11 Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.

We can enter into the rest on any matter of our lives, the labour is in the word, not religious activities. When you enter into rest of your health, you will be full of peace and joy even in the face of challenges, you will say, "I am well able to take the land". Just like Caleb and Joshua. 

When Jesus taught on the above scripture, the people's response was, "what is the work of God that we may do it? Jesus simply just answered them: John 6:29 Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent. 

This implied that, the real labour is for doubt to be cleared and faith sustains in us. This is what is called the fight of faith. You stand on God's word and His promises through meditation and confession until doubt is eliminated concerning your desires.