What about the Giants like Goliath? Is there any record outside the Bible
that describes them? And how can I explain 2 Samuel 21:19?

I suppose you will find some one who will claim that some obscure
reference to giants in the literature of the Assyrians or the Egyptians or
so forth supports the Biblical description of giants, or of the Nephilim
(Genesis 6:4), which seem to be a people who were very large. The problem
with such “support” is that this sort of evidence also supports belief in
unicorns, dragons and all kinds of other mythical creatures.

As far as I know, there is no legitimate, hard evidence to support the
existence of a race of very unusually tall people in ancient times.
Goliath himself appears to be a single, very unusually large man. Perhaps
he had some sort of genetic abnormality. Genetic abnormalities which
create unusually large people are rare but are known to occur. Even if a
paleontologist or anthropologist were to dig up one particularly large
skeleton from several thousand years ago, it is hard to say that this
would particularly support belief in the Nephilim or in the fact that
Goliath was so large. In the end, we are left to accept the existence of
the Nephilim and the very large stature of Goliath on the basis of the
authority of the Bible and its record as an amazingly accurate historical
account. Given the massive evidence in support of the Bible as an inspired
book and in the historical accuracy of the Bible (see: Historical and
Archaeological Evidence Which Supports the Bible), I personally find it
easy to accept the Biblical account on its own authority.

As far as 2 Samuel 21:19, apparently the parallel account in 1 Chronicles
20:5 mentions Lahmi the brother of Goliath, rather than Goliath. Most
likely there is a copyist error in either 2 Samuel 21:19 or 1 Chronicles
20:5. If the scribal error is in 1 Chronicles 20, then this Goliath is a
different one from the one killed by David. More likely, the scribal error
is in 2 Samuel 21:19. Small scribal errors in the Hebrew Old Testament are
not uncommon, but in general they have no significant effect on the
meaning of Old Testament passages. (see: A Remarkable Collection at this
website).

John Oakes, PhD