OF THE CHANGE IN THOMAS To find ways of making David propose to Elspeth, of making Elspeth willing to exchange her brother for David--they were heavy tasks, but Tommy yoked himself to them gallantly and tugged like an Arab steed in the plough.

It should be almost as pleasant to us as to him to think that love was what made him do it, for he was sure he loved Grizel at last, and that the one longing of his heart was to marry her; the one marvel to him was that he had ever longed ardently for anything else.
Well, as you know, she longed for it also, but she was firm in her resolve that until Elspeth was engaged Tommy should be a single man.
She even made him promise not to kiss her again so long as their love had to be kept secret.

"It will be so sweet to wait," she said bravely.

As we shall see presently, his efforts to put Elspeth into the hands of David were apparently of no avail, but though this would have embittered many men, it drew only to the surface some of Tommy's noblest attributes; as he suffered in silence he became gentler, more considerate, and acquired a new command over himself.

To conquer self for her sake (this is in the "Letters to a Young Man") is the highest tribute a man can pay to a woman; it is the only real greatness, and Tommy had done it now.