I. The blessed man is described in this verse by negatives. We are told what he does not do. It so happens that we cannot understand some of the very highest things in life except they are put to us in precisely this way. There are more ways of saying "Thou shalt not" than there are of saying "Thou shalt."
II. But a man who is thus instructed in negatives occupies a very peculiarly perilous position. Man has energies; he must be doing something, must be affirmative, practical, energetic. Therefore we await some further instruction as to the way in which to direct our life. We have it in ver. 2: "His delight is in the law of the Lord, and in His law doth he meditate day and night." God does not destroy our powers; He does not quench our aspirations and turn us into nonentities. He lays His hand upon the strength we are misusing and says, "You must use this strength in another direction and for another purpose." What is the happy man doing? He delights in the law of the Lord.
III. What will be the consequence of this delight? "He shall be like a tree," etc. Beauty is always associated with righteousness in the highest quarters. Then there comes the great promise, "Whatsoever he doeth shall prosper." The great principle of the text is right as honour, truth as crown, goodness occupying the throne.
IV. "The ungodly are not so," etc. The sinner has a brief day. There is no life in the ungodly that abides; there is surface, there is no vitality; there is an outward attitude and display of comfort and enjoyment, but there is at the heart that which will give way under pressure.
Parker, City Temple,vol. iii., p. 289.
References: Psalms 1:1. E. C. Wickham, Wellington College Sermons,p. 203; A. Mursell, Christian World Pulpit,vol. xxvi., p. 269; C. C. Bartholomew, Sermons chiefly Practical,p. 245.