The giants in the Bible of which Goliath was one, are a species not directly created by God. When David hit him with the stone, Goliath did not immediately die, but was just stunned. Quickly after being hit, David slew him, but still he was not dead. Then he finished him off by cutting his head off. It was not easy to kill him. God created the flood in Noah's day to wipe the giants out, but there even still remained a few after a flood which were subsequently finally erradicated. Today, they are gone. People who are extra tall today are not those giants of old.

When the Tribulation comes, it will be like Noah's day, and we might expect also a species of man that is the strangest of sorts. This may involve genetic alterations and other kinds of mutations or enhancements.

How did these giants come about? When demons partook in marriage with daughters of men, this strangest of unions caused these new species of men which are physical descendants of evil spirits, a race of beings that became disembodied in Gen. 1.2 when God made the earth desolate and waste due to the sin of earth's earliest ages. They became evil because they chose to follow the path of fallen Lucifer and his angels.

In earth's earliest ages, Lucifer fell out of 3rd heaven with 1/3 of the angels. In the Tribulation, Satan will fall out of 2nd heaven with the angels to be cast down to earth.

In this casting down, these angels will seek to take on the flesh as did the demons do so, not staying in their rightful place and original state. When God split the firmament in day 2, which was not called a good day like the other summary days of restoration, some of those demons came up and did not stay in their place of judgment to be cast into hell one day. One of those demons went into the serpent to tempt Adam and Eve.