2 Prepare the way of the Lord, make his paths straight. Every valley shall be filled, and every mountain and hill shall be brought low; and the crooked shall be made straight, and the rough ways shall be made smooth. What way for the Lord are you supposed to prepare? The way into your heart for him to dwell as the ruling Lord of your thoughts, words, and deeds — a true king that rules everything in your life. Think about it — to make the Lord's paths straight, level, and smooth, is to cleanse your heart and body so the Lord can dwell and walk in you, for he would have you to be the temple of the living God. This is an individual preparation of man, the prerequisite to salvation.
In his Journal, George Fox wrote of seeing within himself the mountains burning up, the way made straight, etc:
"I saw also the mountains burning up, and the rubbish, and the rough, and crooked ways and places made smooth and plain, that the Lord might come into his tabernacle. These things are to be found in man's heart; but to speak of these things being within, seemed strange to the rough, crooked, and mountainous ones.* Yet the Lord said, ‘0h earth, hear the word of the Lord!’"
*the rough, crooked, and mountainous ones are those people who have not experienced the cleansing power of the Lord, which cleansing is experienced when you persistently sit, wait, watch, listen, hear, and obey what the Lord commands you to do.
Fox also has a detailed writing, which describes the mirror of the earth in every man's heart; see A Word From the Lord, to All the World.
A man cannot prepare his own heart; it must be prepared by the changing power of God's grace, which power is accessed by you going to him. You must wait on him — listen silently, with the humility of a sinner in need of his changing power — grace. You must wait, listen in silence, hear, and obey, thus to receive with meekness the engrafted word, which is able to save your souls. James 1:21. So wait, watch, listen, hear, obey... wait, watch, listen, hear, obey..... seek, listen, obey. Do this repeatedly, follow his commands, and his words that you hear him speak to you will impart the life of God to you, as he removes the sins from your heart, one by one. To deny yourself is to deny your own will and do God's will; to follow is to obey the commands you hear him speak to you: this is to deny yourself, pickup your cross, and follow Jesus — the inward cross of self-denial, which puts to death your selfish spirit, to be replaced by the Spirit of Christ.
And all flesh shall see the salvation of God. Note! This will be done for all flesh, in this life through the inward cross of self-denial, or in the next life with a man's part in the lake of fire, (see Is There Hope for All for more on this subject); and then all flesh will see the salvation of God for salvation is to be delivered from sin.