# expecting nothing in return

"not expecting the person to return what you have given him" or "not expecting the person to give you anything"

# your reward will be great

"you will receive a great reward" or "you will receive good payment" or "you will get good gifts because of it"

# you will be sons of the Most High

It is best to translate "sons" with the same word your language would naturally use to refer to a human son or child.

# sons of the Most High

Make sure that the word "sons" is plural so it is not confused with Jesus' title "The Son of the Most High."

# unthankful and evil people

"people who do not thank him and who are evil"