From the SUB TUUM blog:
Joseph’s character and qualities can be deduced from the fact that God honored him with the title of father, and, although his doing so was a mere matter of convenience, this was what he was known as and believed to be. Joseph’s own name, which, as you know means “increase,” supplies further indications. Call to mind the great patriarch of old who was sold into Egypt, and you will realize that it was not only his name that our saint received but also his chastity, innocence, and grace.
His brothers’ envy had caused the earlier Joseph to be sold and taken to Egypt, thus symbolizing the selling of Christ: the later Joseph carried Christ into Egypt, fleeing before Herod’s envy. The former Joseph kept faith with his master and would not become involved with his master’s wife, while his namesake faithfully protected his own spouse, the mother of his Lord, acknowledging her virginity and remaining continent himself. The first Joseph had the gift of interpreting dreams: the second was given a revelation of the divine plan and a share in its accomplishment. Joseph the patriarch stored up grain, not for himself but for all the people: our Joseph was given custody of the living bread from heaven to keep safe both for himself and the whole world.
There is no doubt that the Joseph to whom the Savior’s mother was engaged was a good and faithful man. He was, I say, the wise and faithful steward whom the Lord appointed to support his mother and care for himself in childhood, singling him out for his complete reliability to help him with his momentous plan.
Added to all this, scripture tells us that he was of David’s house. Joseph was obviously of David’s house, a true descendant of the royal line, a man of noble birth and still nobler disposition. That he was David’s son was seen from the fact that he in no way failed to maintain his standard: he was a true son of David not only as regards physical descent, but also in his faith, holiness, and devotion. In him the Lord found, as it were, a second David, a man after his own heart, to whom he could safely confide his most holy and secret design. To him as to another David he revealed the unfathomable, hidden depths of his wisdom, and granted him knowledge of that mystery which was known to none of the princes of this world. In a word, that which many kings and prophets had longed to see and had not seen, to hear and had not heard -that was granted to Joseph. He was allowed not only to see and hear him, but also to carry him, guide his steps, embrace and kiss him, cherish and protect him.
It is not only Joseph, however, but Mary as well whom we believe to be a descend- ant of David, for she would not have been engaged to a man of David’s line unless she herself had been of that line. Both of them, then, belonged to David’s family, but it was in Mary that the oath which the Lord had sworn to David was fulfilled, while Joseph was privy to the promise and witnessed its fulfillment.