"Perfect is His work": His work is whole with all creatures, and His ways are not to be brought into question. The slightest variation is not to be entertained regarding them — "If I had three eyes," "If I had three hands" "If I had three feet," "If I could walk on my head," "If my face faced backwards" — "how wonderful it would be!" This is the intent of "Perfect is His work."
"for all of His ways are justice": He sits in judgment with everyone and gives him what he deserves. "a faithful G-d": He believed in the world and created it.