In Macbeth, after the encounter with Macdonwald, what the is next trouble that Scotland faced (lines 25-42)?

Your question is refering to Act I scene 2, which is when
King Duncan is awaiting news of the battle that is being fought by his forces, and a
wounded messenger arrives to give them a fresh update on the state of play. After the
encounter with Macdonwald and his forces with Macbeth and his Scottish troops, the next
issue that threatened Duncan's forces was a renewed assault by the King of Norway that
had the potential to overwhelm the Scottish forces. Note how the messenger describes
this event:

readability="18">

No sooner justice had, with valour
arm'd,

Compell'd these skipping Kernes to trust their
heels,

But the Norweyan Lord, surveying
vantage,

With furbish'd arms, and new supplies of
men,

Began a fresh
assault.

However, in spite of
the threat that this renewed vigour of the enemy represented, it was not enough to make
Banquo and Macbeth afraid, and this vigour of the enemy only inspired them to strengthen
their own attack, leading to their ultimate victory.