Firm (4731) (stereos) means stable (firmly established), steadfast or solid like a foundation. In a physical sense this word describes something as firm, hard, solid and compact like a rock. It is used of food adults eat (solid) rather than milk, the former referring to advanced or deeper doctrine. Stereós is used 4x in NT (1x 2Ti; 2x Heb; 1x 1Pe) and is translated as (firm, 2; solid, 2). There are 14 uses in the LXX (Exod. 37:17, 20; Num. 8:4; Deut. 32:13; 1Sa 4:8; Ps. 35:10; Is. 2:21; 5:28; 17:5; 50:7; 51:1; Jer. 15:18; 30:14; 31:11) 2 Timothy 2:19 (note) Nevertheless, the firm (figuratively = solid, rigid, strong) foundation of God stands, having this seal, "The Lord knows those who are His," and, "Let everyone who names the name of the Lord abstain from wickedness." Hebrews 5:12 (note) For though by this time you ought to be teachers, you have need again for someone to teach you the elementary principles of the oracles of God, and you have come to need milk and not solid food...5:14 But solid food is for the mature, who because of practice have their senses trained to discern good and evil. 1 Peter 5:9 But resist him, firm (figuratively = steadfast or immovable in one's beliefs) in your faith, knowing that the same experiences of suffering are being accomplished by your brethren who are in the world. The idea Peter is conveying is that they are to be steadfast (firmly fixed in place, not subject to change) immovable (not moving or not intended to be moved) in their faith. Christians are to stand firm and unyielding, resisting the devil. Wuest adds that steadfast ("firm") is "a military term. Paul uses it in Colossians 2:3 (see note) when he says “beholding your order,” that is, “beholding your solid front or close phalanx.” The Greek phalanx was a body of heavy-armed infantry formed in ranks and files close and deep. Pope has a line, “The Grecian phalanx, moveless (without movement thus picturing their stability and immovability against enemy assaults) as a tower.” The word speaks of solidity in the very mass and body of the thing itself." (Wuest, K. S. Wuest's Word Studies from the Greek New Testament: Eerdmans) J Vernon McGee adds that The picture here is of an army standing against an enemy. We should stand with other believers. I do not think you can resist the Devil by yourself. You not only need the armor of God, but you will also need other believers to stand with you. That is the reason that whenever I have need, I let all the listeners to my radio broadcast know about it. I want them to stand with me in prayer—we need to do that. (McGee, J V: Thru the Bible Commentary: Thomas Nelson) Soldiers had to maintain their ranks and formation or the enemy would attack them from the side or from behind. Using a word related to the adjective stereós, Paul writes to the Colossians that "even though I am absent in body, nevertheless I am with you in spirit, rejoicing to see your good discipline (standing shoulder to shoulder in such orderly array) and the stability (the firmness and the solid front) of your faith in Christ." (See note Colossians 2:5) . Paul actually uses two military terms in this verse, the first "good discipline" (taxis) picturing the Colossian saints arranged like an army in ranks, with each soldier in his proper place prepared for attack. "Stability" (stereoma from stereós) describes a solid front of soldiers. As Vincent says their "Faith is represented as a host solidly drawn up: your solid front, close phalanx”. Their faith in Christ was like the solid part of a military line which can and does stand the attack of the enemy, in this case false teachers. As Eadie notes their faith reposed on Christ—as unshaken as its object. His love never wavers, His power never fails, His fidelity never resiles (retracts, recoils) from its pledge. And those unseen blessings which faith surveys are unchanging in their certainty and glory. The portals of heaven are never barred—its living stream is never dried up; the pearls of its gates are unsoiled, nor is the gold of its pavement ever worn through. Surely, then, faith ought to be as stedfast as the foundation on which it rests, and the object which it contemplates and secures. Paul used stereós in his letter to Timothy writing that even though their were some men who had "gone astray from the truth saying that the resurrection has already taken place, and they upset the faith of some, nevertheless the firm (stereós - solid, sure, unshaken) foundation of God stands, having this seal, "The Lord knows those who are His," and, "Everyone who names the name of the Lord is to abstain from wickedness." (See notes 2 Timothy 2:18; 2:19) "Copy and paste the address below into your web browser in order to go to the original page which will allow you to access live links related to the material on this page - these links include Scriptures (which can be read in context), Scripture pop-ups on mouse over, and a variety of related resources such as Bible dictionary articles, commentaries, sermon notes and theological journal articles related to the topic under discussion." http://www.preceptaustin.org/1_peter_59.htm#firm