# He is secure at all times

"He is safe at all times." He is not really safe, but he thinks that he is.

# your righteous decrees are too high for him

"he cannot understand your righteous decrees"

# he snorts at all his enemies

"he thinks that all his enemies are weak and worthless" or "he sneers at all his enemies" 

# he snorts

This means that he blows air out noisily through his nose.