My Belief of this, induces me to hope, though I must not presume, that the same Goodness will still be exercised towards me in continuing that Happiness, or in enabling me to bear a fatal Reverse, which I may experience as others have done: the Complexion of my future Fortune being known to him only and in whose Power it is to bless to us even our Afflictions.
How to understand this sentence, it is quite complicated for me.
This writing is somewhat archaic.
"him only" = God. It is known only to God.
God has the power to bless (for us) even our afflictions.
So, the person's future is known only to God, who, if He chooses, can relieve the person from his afflictions.
known to him only and in whose Power it is to bless to us even our Afflictions.
Raymott: So, the person's future is known only to God, who, if He chooses, can relieve the person from his afflictions.
Raymott's interpretation is in error here.
Note how the phrase is, "to bless to us even our Afflictions".
God may bless us with good fortune; but he may also 'bless' us in permitting us to suffer misfortune and physical afflications (as with Job in the Christian bible) that the person may learn and deepen his trust in God's wisdom.