I have now come here on the deck of a ship, and now you shall know how you might think in your heart about the heartfelt love of my lord. (8b-11a)
The messenger has come to the lady hoping to effect a change in her state of mind. He wants her to feel sure of her lord's love. Here he promises that the lady <em>will</em> feel that way. He's very sure of himself, this guy (or piece of wood).
I dare promise that you will find there a gloriously assured commitment. (11b-12)
Saying that he "dare" promise the lady's going to find a commitment in her and her lord's heart acknowledges that the outcome of his message is far from certain, despite the confidence of the previous lines.
Begin to seek the ocean, the native land of seagulls, board a seaworthy ship so that south from here you may find the man beyond the ocean-path, where your lord is in expectation of you. (26-29)
Saying that her lord is already "in expectation" of her implies that he, like the speaker, is optimistic about the effect his message will have upon the lady.
Nor can he in all the world desire . . . more in his mind, as he told me, than that the all-ruling God might grant that you two . . . together may afterwards [give] to men and to retainers, studded circlets. (30-35a)
The lord eagerly anticipates the time when he and his lady will be together again, presiding over a hall. The distribution of wealth to his subjects was one of the most important displays of an Anglo-Saxon lord's power. By anticipating his lady's participation in this ritual, the lord is indicating his desire to make her his legitimate queen, not just his lover. The future he is offering her is looking pretty good.
Now the man has overcome his trouble; he has no lack of joy, or of horses or treasures, or the pleasures of mead, or any of the noble treasures upon earth, prince's daughter, if he possess you. (44-48)
Although the lord offers his lady a place at his side as ruler, this passage suggests that the messenger views them as far from equal. The messenger obviously sees the lady as yet another of his lord's numerous possessions. The future that lays ahead for her, at least from the speaker's point of view, is therefore one of both power and subjection.