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. John 6:27

Jesus says; Labor not for the meat (life) that your own hands can give you (that the world can give you), that perishes.

But for the meat (life) that endures...

This word endures in John 6:27 means: (enduring) To remain, to abide, to continue, to stay.

He says that the meat He gives remains, abides and continues unto Eternal life.

So what continues? You or the meat (the Word of life) that He gives? The meat, Jesus said is what endures unto eternal life.

In the same chapter, we have the feeding of the 5000. And it says that OF the ones who ate (the bread) and were satisfied, he gathered and lost nothing (they had 12 baskets full leftover). This is a shadow of what He says later in the chapter.

He says those who eat this meat, this bread of life, when they are drawn by the Father (and I am adding for emphasis) "and are satisfied", of those He loses nothing.

There are many (even in Churches) eating from another word (a perishable word) and they are never satisfied. The Word made flesh in Jesus is the only word that satisfies. It is the Word that the Father has given to draw men’s hearts.

And Jesus said "that all which He (the Father) has given Me (gathered), I should lose nothing" John 6:39

Jesus says at the end of the chapter that there are some of you that believe not. And that no man comes to Him unless the Father draws him.

He says I called all twelve of you but one of you is a devil (born of the word of the serpent/the word that perishes). Notice all are called but not all believe on the Word of eternal life.

All those who rely on their own works (the meat that perishes) are living a cursed life (death); because they continue in all those things that can never justify them unto life. When you eat from the bread of life and are satisfied, you cease from eating, from relying on the works of your own hand.

The Word of life is the meat that satisfies wherein you rest from your labors.

The Word of life is the only meat that remains, abides and continues in you unto Eternal life.

For Him has God sealed with Eternal life.

4972 /sphragízō ("to seal") signifies ownership and the full security carried by the backing (full authority) of the owner. "Sealing" in the ancient world served as a "legal signature" which guaranteed the promise (contents) of what was sealed.
For in Him has God sealed/guaranteed the promise of eternal life that was from the beginning.

The gospel or the good news contained in Jesus Christ, the Word of eternal life made flesh, is a certainty!!