Algernon, it would be helpful to know how long ago this happened - is it a reaction to an immediate loss? The passage mentioned is from St John's Gospel, notably at 14:14 but is mentioned elsewhere as well. First, we must acknowledge that the passage is difficult and is central to the problem of apparently unanswered prayer. It is a trite observation that we have to ask in Christ's Name and for things which are for the benefit of our soul and its salvation. But there are times when we ask for something which from any point of view seems right and we pray to Christ with our whole being but what we ask for does not happen. This is especially hard when the matter concerns bereavement, and I well recall grappling with this when my wife died from cancer thirteen years ago.
When a loved one has a terminal illness, what ought we to pray for? A miracle of healing? This is not wrong but what if healing is not God's will? What we should pray for is that God will grant the dying person the grace to bear the illness and make ready for an entrance into the Kingdom of Heaven. After all, the greatest miracle is our salvation in Christ, and it is the healing of the soul which matters, not the healing of the body. We should also pray for grace that we left behind will bear our loss. But it is not all loss: our loved one enters Christ's Kingdom - can we not be glad for them that they are where we all aim to go? And what if our loved one goes there before us - can we rail against God and prefer that out loved one should not be with Him but still with us? I don't know what you mother's age was but it must be admitted that it is natural for parents to pass away before their children; consider how hard it is for parents who bury a child as my late wife's mother had to. But we have to face bereavement in Christ. If we pray in His Name for consolation, will He not give it? But we have to pray in humility: if we are bitter at heart, we cannot pray in His Name, and that bitterness will block our prayer.
For everyone, there is a time to depart this life and go to God, and we could wish for nothing better for anyone than being closer to God than is possible in this life. Writing a letter of consolation to parents whose only son had died, St Basil the Great said, 'earth has not covered our beloved but heaven has received him'.