Thou art near in their mouth - They have no sincerity: they have something of the form of religion, but nothing of its power.
Albert Barnes
Notes on the Whole Bible
Their veins - i. e., their heart. The reins were regarded by the Jews as the seat of the affections.
Matthew Henry
Concise Bible Commentary
When we are most in the dark concerning God's dispensations, we must keep up right thoughts of God, believing that he never did the least wrong to any of his creatures. When we find it hard to understand any of his dealings with us, or others, we must look to general truths as our first principles, and abide by them: the Lord is righteous. The God with whom we have to do, knows how our hearts are toward him. He knows both the guile of the hypocrite and the sincerity of the upright. Divine judgments would pull the wicked out of their pasture as sheep for the slaughter. This fruitful land was turned into barrenness for the wickedness of those that dwelt therein. The Lord reproved the prophet. The opposition of the men of Anathoth was not so formidable as what he must expect from the rulers of Judah. Our grief that there should be so much evil is often mixed with peevishness on account of the trials it occasions us. And in this our favoured day, and under our trifling difficulties, let us consider how we should behave, if called to sufferings like those of saints in former ages.
They have taken root. A figure denoting the prosperous state of the wicked.
Their reins. Literally, “the kidneys.” These organs were considered to be the seat of the emotions. Hence by “reins” were designated “the inner feelings” (see Ps. 26:2).