What does 'to pass from dream to grander dream' mean?

Directions: Read the following passage carefully and answer the question that follows:

Progress in life depends a good deal on crossing one threshold after another. Some time ago, a man watched his little nephew trying to write his name. It was hardwork, very hardwork. The little boy had arrived at an effort threshold. Today, he writes his name with comparative ease. No new threshold confronts him. This is the way with all. Conquer one difficulty, a new difficulty appears or should appear. Some people make the mistake of steering clear of thresholds. They avoid anything that requires genuine thinking and use of energy. They prefer to stay in a rut where thresholds are not met. Probably they have been at their job a number of years; things are easy for them. They make an effort to seek out new obstacles to overcome. Real progress stops under such circumstances. 
Some middle–aged and elderly people greatly enrich their lives by continuing to cross thresholds. One man went into an entirely new business when he was past middle-age and made a success of it. De Morgan did not start to write novels until he was past sixty. Psychologists have discovered that man can continue to learn throughout the life and it is undoubtedly better to try and fail than not to try at all. Here, one can be placed in the category of the Swiss mountaineer of whom it was said that he died climbing. When a new difficulty rises to obstruct your path, do not complain. Accept the challenge. Determine to cross this threshold as you have crossed numerous other thresholds in your past life. In the world of the poet, do not rest. Strive to pass from dream to grander dream.