“And this is the will of him who sent me, that I should lose nothing of all that he has given me, but raise it up on the last day.”John 6:39
This promise is highly necessary for us, who miserably groan under so great weakness of the flesh, of which every one of us is sufficiently aware; and at every moment, indeed, the salvation of the whole world might be ruined, were it not that believers, supported by the hand of Christ, advance boldly to the day of resurrection. Let this, therefore, be fixed in our minds, that Christ has stretched out his hand to us, that he may not desert us in the midst of the course, but that, relying on his goodness, we may boldly raise our eyes to the last day.
There is also another reason why he mentions the resurrection. It is because, so long as our life is hidden in Christ (Colossians 3:3) we are like dead men. For in what respect do believers differ from wicked men, but that, overwhelmed with afflictions, and like sheep destined for the slaughter (Romans 8:36), they have always one foot in the grave, and, indeed, are not far from being continually swallowed up by death? Thus there remains no other support of our faith and patience but this, that we keep out of view the condition of the present life, and apply our minds and our senses to the last day, and pass through the obstructions of the world, until the fruit of our faith at length appear.
John Calvin, Commentaries, 253–254