I don't believe this line is necessarily prophetic on Hamlet's part. In this soliloquy he is lamenting and struggling with the fact that his mother married his uncle within a month of King Hamlet's death. Unlike his mother, his uncle, and others in the play, Hamlet recognizes that for his mother and uncle to marry so quickly is an unusual and extremely disturbing circumstance. In this line, Hamlet is simply stating that this marriage is not good, and good can never come from such a union because of the manner in which it came about.
Hamlet’s last words of his first soliloquy are the voice of his conscience and certify him a seer.
Actually, Hamlet is not rascal, but he is scholar and his faculty of thinking is not feeble. He is a great lover of his parents. His mother’s speedy marriage with his uncle has plunged him into great mire. He condemns it because it is escorting him to deep sorrows and the world seems useless to him. As he says:
How weary, stale, flat and unprofitable
Seem to me all the uses of the world.
His father loved her too much and was a great shield to sorrow not to inflict her. He loved her spiritually and emotionally. She was always clung to him. As he says:
So loving to my mother
That he might not between the winds of heaven
Visit her face to roughly.
There was a huge love and how it decoyed. His father’s death passed two months, she married an other person. So it was a great humiliation to him and the true love of his father.
He condemns his mother and sees the dark future. The marriage is on deception and treachery that is against spirituality .In it there is the sense of beast. His uncle is a satyr like, who is sensual and ugly. This bond seems for time being and unfair.
This fleshy marriage, may be shelter, has caused of the bed of thorns to Hamlet. Each moment brings a new shock to him. It is his prophecy that marriage based on selfishness, deception and sensuality, its end is very bad. So it is symptom of disaster may be following.