Roman infantrymen wore tough sandals studded with sharp, thick nails on the bottoms to increase traction.  The gospel that has brought peace to the Christian enables him or her to stand firmly against temptation. Likewise the gospel is what enables us to move forward against our enemies (cf. Isaiah 52:7). The preparation of the gospel of peace probably refers to the gospel the Christian soldier has believed that enables him to stand his ground when attacked. We must be so familiar with the gospel that we can share it with others (cf. 1 Peter 3:15). That grip on the gospel will enable us to hold our ground and even advance when tempted. The gospel in view is the whole Christian message viewed as good news, not just how to become a Christian. [source][source][source]
". . . protection comes from reflecting the unity that the gospel provides within the community ("shod your feet with the preparation of the gospel," Ephesians 6:16, looks back to Ephesians 2:11-22; it is not a reference to evangelism)." [source]
Ephesians 6:13-24 - "finally, Be Strong In The Lord"
Many would be strong, but fail because they forget that they can be effectively so only "in the Lord, and in the strength of His might." Paul had a very vivid conception of the powerful forces that are arrayed against the Church. He is not dealing here especially with our personal temptations, but with those hosts of wicked spirits that lie behind the evil of the world. It is probable that the vast systems which oppose the gospel-the philosophies, temples, and priests of false religions; the trade in strong drink, impurity, and like evils; and such iniquitous institutions as the system of indentured slavery-are directly promoted and furthered by the agency of evil spirits in arms against God.
We must be pure and holy, if we are to prevail against evil; and especially must we give ourselves to prayer. To prevail in this warfare we must diligently employ the weapon of all prayer. Tychicus carried this letter. He was faithful to the end, Acts 20:4; 2 Timothy 4:12. The Epistle closes, as it began, with uncorrupted, that is, pure and eternal, love. Alford says, "This is the only truth worthy to be the crown and climax of this glorious Epistle." [source]
Chapter Summary: Ephesians 6
1The duty of children toward their parents; 5of servants toward their masters 10Our life is a warfare, not only against flesh and blood, but also spiritual enemies 13The complete armor of a Christian; 18and how it ought to be used 21Tychicus is commended
What do the individual words in Ephesians 6:15 mean?
Greek Commentary for Ephesians 6:15
“Having bound under” (sandals). First aorist middle participle of υποδεω hupodeō old word, to bind under (Mark 6:9; Acts 12:8, only other N.T. example). [source]
Late word from ετοιμαζω hetoimazō to make ready, only here in N.T. Readiness of mind that comes from the gospel whose message is peace. [source]
Only here in the New Testament. The Roman soldier substituted for the greaves of the Greek (metal plates covering the lower part of the leg) the caligae or sandals, bound by thongs over the instep and round the ankle, and having the soles thickly studded with nails. They were not worn by the superior officers, so that the common soldiers were distinguished as caligati. Ἑτοιμασία means readiness; but in Hellenistic Greek it was sometimes used in the sense of establishment or firm foundation, which would suit this passage: firm-footing. Compare Isaiah 52:7. [source]
Reverse Greek Commentary Search for Ephesians 6:15
Indirect middle (by yourself or for yourself) first aorist imperative of υποδεω hupodeō to bind under, old verb, only three times in the N.T. (Mark 6:9; Acts 12:8; Ephesians 6:15 (middle). Sandals (σανδαλια sandalia). Persian word common from Herodotus on, a sole made of wood or leather covering the bottom of the foot and bound on with thongs. In the N.T. only here and Mark 6:9. In the lxx used indiscriminately with υποδημα hupodēma Cast about thee Second aorist middle (indirect) imperative of περιβαλλω periballō old and common verb to throw around, especially clothing around the body as here. The ιματιον himation (outer garment) was put over the χιτων chitōn It was not a hurried flight. Follow me (ακολουτει μοι akolouthei moi). Present (linear) active imperative, keep on following me (associative instrumental case). [source]
Emphasizing the rapid approach of the messenger. “In their running and hastening, in their scaling obstructing mountains, and in their appearance and descent from mountains, they are the symbols of the earnestly-desired, winged movement and appearance of the Gospel itself” (Lange). Compare Nahum 1:15; Ephesians 6:15; Romans 3:15; Acts 5:9. Paul omits the mountains from the citation. Omit that preach the gospel of peace. [source]
Better, the God of peace himself. God's work is contrasted with human efforts to carry out the preceding injunctions. The phrase God of peace only in Paul and Hebrews. See Romans 15:33; Romans 16:20; Philemon 4:9; Hebrews 13:20. The meaning is, God who is the source and giver of peace. Peace, in the Pauline sense, is not mere calm or tranquillity. It is always conceived as based upon reconciliation with God. God is the God of peace only to those who have ceased to be at war with him, and are at one with him. God's peace is not sentimental but moral. Hence the God of peace is the sanctifier. “Peace” is habitually used, both in the Old and New Testaments, in connection with the messianic salvation. The Messiah himself will be Peace (Micah 5:5). Peace is associated with righteousness as a messianic blessing (Psalm 72:7; Psalm 85:10). Peace, founded in reconciliation with God, is the theme of the gospel (Acts 10:36). The gospel is the gospel of peace (Ephesians 2:17; Ephesians 6:15; Romans 10:15). Christ is the giver of peace (John 14:27; John 16:33). [source]
The phrase N.T.o Ἑτοίμος readyonly here in Pastorals. Comp. ἑτοιμασία readinessor preparation, Ephesians 6:15(note). [source]