As Richard Dalloway walks home from the flower shop, he repeatedly reassures himself that he’ll tell Clarissa that he loves her when he gets home—and though it seems as if he has every intention of doing so, the mere fact that he keeps repeating his intentions to himself suggests that he knows, on some level, that he won’t be able to actually express his feelings once he’s face to face with his wife. The repetitions thus foreshadow his eventual failure to tell Clarissa what he wants to tell her.
After buying the flowers, he imagines greeting her "with his great bunch [of flowers] held against his body" and saying "straight out in so many words (whatever she might think of him), holding out his flowers, ‘I love you.’ Why not?” The phrase "why not?" hints that Richard has trouble saying "I love you" but is trying to get himself to see it as an easy, painless thing to do. On the very same page, the narrative once again reminds readers what, exactly, Richard is doing:
Here he was walking across London to say to Clarissa in so many words that he loved her.
Needless to say, readers already know what he's doing—it is, after all, a simple task. And yet, Richard clearly sees it as something rather difficult, considering that he keeps reminding himself that he's going to give Clarissa flowers and tell her that he loves her. "But he would tell Clarissa that he loved her, in so many words," the narrator says yet again just a few pages later. The phrase "in so many words" foreshadows his eventual failure to say anything at all along the lines of "I love you." Despite his convictions, it's clear that Richard has already started backing down before he even gets home, subconsciously preparing to let himself off the hook by telling himself that he'll say "I love you" in so many words—that is, he has already accepted that he probably won't actually be able to say "I love you," so he decides that his efforts will still count for something as long as he says something along the lines of "I love you."
Sure enough, when he finally gets home and greets Clarissa, he fails to say what he wanted to say:
He was holding out flowers — roses, red and white roses. (But he could not bring himself to say he loved her; not in so many words.)
The narrative subtly pokes fun at Richard in this moment by noting that he can't even say what he wanted to "in so many words," playing on his previous plan to at least express some sort of romantic sentiment. All he does, then, is give Clarissa flowers, thus highlighting how difficult he finds it to communicate openly with his wife about his feelings—an inability that the narrative has already foreshadowed quite heavily.