He is referring to Isaiah 52:7. "How beautiful upon the mountains are the feet of him that bringeth good tidings, that publisheth peace; that bringeth good tidings of good, that publisheth salvation; that saith unto Zion, Thy God reigneth!" Therefore, the feet are the feet of a messenger in the prophecy. In the original context, the messenger is to God's people, and his message is the good news that God is returning [52:8] "Thy watchmen shall lift up the voice; with the voice together shall they sing: for they shall see eye to eye, when the Lord shall bring again Zion." his exiled and scattered people to their homeland, out of the oppression of the Babylonians [52:4-5]. "For thus saith the Lord God, My people went down aforetime into Egypt to sojourn there; and the Assyrian oppressed them without cause. Now therefore, what have I here, saith the Lord, that my people is taken away for nought? they that rule over them make them to howl, saith the Lord; and my name continually every day is blasphemed." But the same chapter [vv.13-15] foreshadows the overflowing nature of the prophecy, pointing to a servant "exalted ... very high", yet "marred more than any man" who shall "sprinkle [with his blood] many nations". In other words, this prophecy is directed finally at the Church gathered out of all lands and peoples, and at the crucified Christ.
So, we are to gladly proclaim our faith in Christ both to our fellow believers, for their encouragement, and to those yet to become so, to draw them in. Does this mean that we cannot be spiritual warriors unless we are evangelists, preachers? No, St Paul calls specific people evangelists, and notes that this is a gift for "some" [Ephesians 4:11], "And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers;" not all, like every gift of the Spirit [1 Corinthians 12]. "For to one is given by the Spirit the word of wisdom; to another the word of knowledge by the same Spirit; To another faith by the same Spirit; to another the gifts of healing by the same Spirit; To another the working of miracles; to another prophecy; to another discerning of spirits; to another divers kinds of tongues; to another the interpretation of tongues: But all these worketh that one and the selfsame Spirit, dividing to every man severally as he will. For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ.
But we must all be prepared to witness to our faith when the opportunity arises. That is why St Paul speaks of the "preparation" of the gospel of peace. The Greek word here is hetoimasia, meaning preparedness, readiness. It is based on the same root word as St Peter uses in his first letter, here: "Always be ready (hetoimoi) to give a defence to everyone who asks you a reason for the hope that is in you, with gentleness and reverence" [1 Peter 3:15] "But sanctify the Lord God in your hearts: and be ready always to give an answer to every man that asketh you a reason of the hope that is in you with meekness and fear:". That translates to three obligations in this area.
One, outsiders should know that we are people of hope, because of what we do and say. Hence, our faith should not be a secret, even if we are not preachers, and our behaviour and attitude should speak hopefulness. They should sense something of another, better world.
Two, we should reflect upon our personal faith intelligently, and defend it with reasons. Christianity is not, contrary to common misconceptions, about believing things for no reason. Both our Lord and the Apostles and Evangelists often appeal to evidence, such as miracles and Creation itself [e.g., John 14:11, "Believe me that I am in the Father, and the Father in me: or else believe me for the very works' sake." Acts 1:3, "To whom also he shewed himself alive after his passion by many infallible proofs, being seen of them forty days, and speaking of the things pertaining to the kingdom of God:" Romans 1:19-20 "Because that which may be known of God is manifest in them; for God hath shewed it unto them.For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:" ]. Interestingly, the Greek word St Peter uses that we translate defence is the same word that is the basis for the term "apologetics", the branch of Christian thought that is devoted to explaining the rational basis for our beliefs. Think about what led you to or strengthened you in our faith, and form your own "testimony". Read Christian apologetics and learn to utilise it. Know where to point people for answers when you're own limitations are reached, but pray that God will transcend those limitations as he works through you anyway.
Three, our defence should be with gentleness and reverence, which means it is a defence of truth without being a personal attack. We must strike the balance between being forthright and being sensitive, as both are necessary.
Let us then, as the Scouts say, "be prepared". We can't all be evangelists like Billy Graham or Bp Patterson (an Anglican missionary martyr) or St Francis of Assisi.
But we can all manifest and defend the Faith, and support one another in it.