Truly it were an excusable covetousness if we did, for affliction is a treasure, and scarce any man hath enough of it. No man hath affliction enough that is not matured and ripened by and made fit for God by that affliction. If a man carry treasure in bullion, or in a wedge of gold, and have none coined into current money, his treasure will not defray him as he travels. Tribulation is treasure in the nature of it, but it is not current money in the use of it, except we get nearer and nearer our home, heaven, by it. Another man may be sick too, and sick to death, and this affliction may lie in his bowels, as gold in a mine, and be of no use to him; but this bell, that tells me of his affliction, digs out and applies that gold to me: if by this consideration of another's danger I take mine own into contemplation, and so secure myself, by making my recourse to my God, who is our only security.
To Donne, it's like an equation. First, we are all the same in that we are all created by God. As such, if someone dies, we all feel it; we are all part of it. If someone is afflicted, we all have an affliction. An affliction brings us closer to the knowledge of God, for suffering, afflictions and death are real parts of our God-given natures. And it is through our awareness of the hardships and afflictions of others that we contemplate our own frailties and susceptibilities and think then of the God who made us all. To suffer and die is to be human, and we are all human.
No man is an island. No one lives alone or dies alone, for we are all one in the eye of God. So says Meditation 17.