Why does Tom have to keep his desire for security and relief "at bay" or in the background?lines 418-420 i read it just do not really understand at...

Having retrieved the yellow sheet which represents weeks
of work,  Tom Benecke loses his balance and knocks into the open window which,
"shuddering," closes on him.  When he is unable to open it, he very carefully draws back
his right hand, and strikes the glass with the heel of his palm.  Unfortunately, his arm
"rebounded" from the pane of glass, causing him to totter, and he realizes he cannot
strike the glass any harder without falling.  In "the security and relief of his new
position" he ponders his situation, disbelief that a single pane of glass can prevent
him from reentering his apartment.  Tom decides that once in his apartment, he will give
release to his feelings, run across the room, jump on the floor, etc. But, now his
desire for this is too strong and "astonishingly intense" and he must keep this feeling
"at bay" while he conserves energy and concentrates upon how he will break the glass. 
He then tries various methods, to no avail.  This is the moment of truth for Tom, for he
cannot wait for Clare and must do something before his grip
weakens.