"And there shall be signs in the sun and in the moon and in the stars, and upon the earth distress of nations with perplexity; the sea and the waves roaring; mens hearts failng them for looking after those things which are coming on the earth: for the powers of heaven shall be shaken. They see the Son of Man coming in a cloud with power and great glory. (St. Luke 21: 25-27)
I thinkl that is a very difficult to understand part of scripture. I don’t know Hebrew. Part of the solution is find out exactly WHAT Hebrew word was used and find out what precise meanings it had.
There WERE “giants” in the earth. Cro-Magnon Man was 6’ tall and probably was mainly a meat-eater. Agriculturalists and pastoralists generally are smaller physically than hunter type people. Even more smaller are old society urban dwellers who oftne lived in squalid quarters, ate poor meals and had bad hygeine.
Read about the first Europeans impression of native American Indians. They often referred to them as “giants”.
On the other hand the word may have a deeper meaning than we can fathom.
The Sons of God and the Daughters of men passage is also very strange.
See:
http://www.gotquestions.org/sons-of-God.html