What is the meaning of "ha'Kel Tamim Darko"?
Radak (here and in Tehilim 18:31): He is Keli (able to do anything); He acts purely and straightly, and pays each person according to his deeds. He returns my virtue (verse 25) and pays my enemies according to their evil.
What is the meaning of "Imras Hashem Tzerufah"?
Rashi: [His word] is clear; He promises and does.
Radak: There is no dross in His judgments; everything is clear and clean. They are all straight and faithful, purified from any impurity.
Malbim (Tehilim 18:31): The Creation, which was via His word, is purified from any impurity. Through this, He is a shield and shelter to all who trust in Him. 1
Malbim: We see Hashem's conduct from two aspects. (a) He made natural laws at the time of the Creation; they do not change. E.g. fire burns, water falls, Shamayim gives dew and the land gives produce. (b) He conducts the world according to deeds of people with choice. When they choose good, He does good to them and sustains them. When their deeds are evil, He arranges the conduct [of His world] for evil. People do not understand the connection between the two methods. Why should rain depend on people's actions? Natural law does not change! Surely Hashem tied the methods together with fine spiritual 'ropes'. A Tzadik is guarded from mishaps; nature is submissive to him, according to his deeds. From the beginning, so Hashem made nature!
