That great and assuring promise of Christ, as explained by the Doctor:
Abraham was like the Lord Jesus Christ Himself who, under the shadow of the cross, and knowing that even His most trusted disciples were suddenly going to leave Him and forsake Him in their fear and concern about saving their own lives, nevertheless was able to say this: 'The hour cometh, yea, is now come, that ye shall be scattered, every man to his own, and shall leave me alone: and yet I am not alone, because the Father is with me' (John 16:32).
According to the Bible, that is the one thing that matters. Our Lord does not promise to change life for us; He does not promise to remove difficulties and trials and problems and tribulations; He does not say that He is going to cut out all the thorns and leave the roses with their wonderful perfume. No; He faces life realistically, and tells us that these are things to which the flesh is her, and which are bound to come. But He assures us that we can so know Him that, whatever happens, we need never be frightened, we need never be alarmed. He puts all that in this great and comprehensive promise: 'Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you.'
- Martyn Lloyd-Jones, Studies in the Sermon on the Mount, p. 457
There are many things He does not promise. But, the one thing He does is the only thing that actually matters.