Isaiah 26:3

“Thou wilt keep [him] in perfect peace, &c.] Peace with God in Christ through his blood, in a way of believing, and as the fruit and effect of his righteousness being received by faith; this is not always felt, received, and enjoyed in the soul; yet the foundation of it always is, and is perfect; and besides, this peace is true, real, and solid; in which sense the word “perfect” is used, in opposition to a false and imaginary one; and it will end in perfect peace in heaven: moreover, the word “perfect” is not in the Hebrew text, it is there “peace, peace”; which is doubled to denote the certainty of it, the enjoyment of it, and the constancy and continuance of it; and as expressive of all…”

“mind . . . stayed-- (Psa 112:7-8). Jesus can create "perfect peace" within thy mind, though storms of trial rage without (Isa 57:19; Mar 4:39); as a city kept securely by a strong garrison within, though besieged without (so Phi 4:7). "Keep," literally, "guard as with a garrison." HORSLEY translates, (God's) workmanship (the Hebrew does not probably mean "mind," but "a thing formed," Eph 2:10), so constantly "supported"; or else "formed and supported (by Thee) Thou shalt preserve (it, namely, the righteous nation) in perpetual peace."”

“26:3 A perfect peace, marked by harmony, quietness, and confidence, is a benefit of the new creation.”

“wilt: Isa 9:6, Isa 9:7, Isa 57:19-21; Psa 85:7, Psa 85:8; Mic 5:5; Joh 14:27, Joh 16:33; Rom 5:1; Eph 2:14-16; Phi 4:7 in perfect peace: Heb. peace peace: mind, or, thought, or imagination stayed: Isa 31:1, Isa 48:2, Isa 50:1 because: Ch1 5:20; Ch2 13:18, Ch2 16:8; Psa 9:10; Jer 17:7, Jer 17:8; Rom 4:18-21 Isaiah 26:4”

“The relation of Israel and Jehovah to one another is now a permanent one. "Thou keepest the firmly-established mind in peace, peace; for his confidence rests on Thee." A gnome (borrowed in Psa 112:7-8), but in a lyrical connection, and with a distinct reference to the church of the last days. There is no necessity to take סמוּ יצר as standing for יצר סמוּך, as Knobel does. The state of mind is mentioned here as designating the person possessing it, according to his inmost nature. יצר (the mind) is the whole attitude and habit of a man as inwardly constituted, i.e., as a being capable of thought and will. סמוּך is the same, regarded as having a firm hold in itself, and this it has whenever it…”