In Julius Caesar, why does Brutus believe that they should confront the other army at Philippi?

The answer to this question can be found in Act IV scene 3
of this excellent tragedy, just after Brutus has heard the news of his wife's death.
When Brutus suggests that they meet Antony's forces at Philippi, it is interesting that
Cassius disagrees, arguing that it is better for the enemy to seek them rather than them
seeking the enemy.

However, Brutus gives two reasons for
why they should meet the enemy at Philippi now. Firstly, the people between Philippi and
where they are now support their forces only grudgingly. Brutus fears that the enemy
would gain extra recruits from them if they marched through their land. Meeting them at
Philippi would prevent this advantage to the
enemy.

Secondly, Brutus thinks that his army is at the
strongest point it can hope to be, therefore it is much better for it to fight now
rather than wait for morale and strength to decline. Note what he
says:

We, at
the height, are ready to decline.

There is a tide in the
affairs of men

Which, taken at the flood, leads on to
fortune;

Omitted, all the voyage of their
life

Is bound in shallows and in
miseries.

On such a full sea are we now
afloat,

And we must take the current when it
serves,

Or lose our
ventures.

Brutus thus argues
that he and his troops must seize the day and fight now when they are at their highest
level in terms of strength, courage and bravery, making the most of "the current when it
serves."