Is the problem the word order? The basic meaning is this:
He held the foe at bay and assured the triumph by his forethought and sacrifice.
The word order, with the clause 'while he gave...' and the placing of 'by his forethought' ahead of the 'of the two succeeding days' may make it harder to understand. It is rhetoric, so try reading it aloud and see if that makes it easier to understand.