The words, “While he was saying this” connect what follows to what has gone on before. Jesus has just challenged his listeners to fill their lives with the kingdom of God, and now a woman in the crowd blesses the mother of Jesus, because of the beauty she sees in Jesus. While Jesus does not deny that his mother is indeed blessed, he uses this opportunity to extend the blessing to anyone who like his mother will hear the Word of God and put it into practice in their lives.
If the woman in the crowd was able to bless the womb that bore Jesus, it was because she could see and experience the goodness in Jesus. This goodness was manifested not only in what he said but in what he did and was therefore visible in his person. If we like Jesus hear the word of God and act on it, then others will pronounce the same blessing on us.