# ride on triumphantly

The writer tells the king to ride his horse or chariot to victory.

# because of trustworthiness, meekness, and righteousness

"in order to fight for what is trustworthy, meek, and right" 

# your right hand will teach you fearful things

"You will learn to accomplish great military feats by fighting in many battles" 

# fearful things

"awesome deeds." This refers to military victories that cause his enemies to fear him and his allies to revere him.