I like the interpretation that Old John Gill makes on this passage.
Again, if two lie together, then they have heat,…. The Targum adds, in the winter; when it is a cold season, they warm one another by lying together. The Targum interprets it of a man and his wife; it is true of others; see 1Ki 1:1;
but how can one be warm alone? not soon, nor easily, in time of cold weather. This is true in a spiritual sense of persons in a Christian communion and religious society; when they are grown cold in their love, lukewarm in their affections, and backward and indifferent to spiritual exercises, yet by Christian conversation may be stirred up to love and good works: so two cold flints struck against each other, fire comes out of them; and even two cold Christians, when they come to talk with each other about spiritual things, and feel one another’s spirits, they presently glow in their affections to each other, and to divine things; and especially if Christ joins them with his presence, as he did the two disciples going to Emmaus, then their hearts burn within them.
We might add:
Pro 27:17 Iron sharpeneth iron; so a man sharpeneth the countenance of his friend.
On the Road to Emmaus
Luk 24:13 And, behold, two of them went that same day to a village called Emmaus, which was from Jerusalem about threescore furlongs.
Luk 24:14 And they talked together of all these things which had happened.
Luk 24:15 And it came to pass, that, while they communed together and reasoned, Jesus himself drew near, and went with them.
Luk 24:16 But their eyes were holden that they should not know him.
Luk 24:17 And he said unto them, What manner of communications are these that ye have one to another, as ye walk, and are sad?
Luk 24:18 And the one of them, whose name was Cleopas, answering said unto him, Art thou only a stranger in Jerusalem, and hast not known the things which are come to pass there in these days?
Luk 24:19 And he said unto them, What things? And they said unto him, Concerning Jesus of Nazareth, which was a prophet mighty in deed and word before God and all the people:
Luk 24:20 And how the chief priests and our rulers delivered him to be condemned to death, and have crucified him.
Luk 24:21 But we trusted that it had been he which should have redeemed Israel: and beside all this, to day is the third day since these things were done.
Luk 24:22 Yea, and certain women also of our company made us astonished, which were early at the sepulchre;
Luk 24:23 And when they found not his body, they came, saying, that they had also seen a vision of angels, which said that he was alive.
Luk 24:24 And certain of them which were with us went to the sepulchre, and found it even so as the women had said: but him they saw not.
Luk 24:25 Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken:
Luk 24:26 Ought not Christ to have suffered these things, and to enter into his glory?
Luk 24:27 And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself.
Luk 24:28 And they drew nigh unto the village, whither they went: and he made as though he would have gone further.
Luk 24:29 But they constrained him, saying, Abide with us: for it is toward evening, and the day is far spent. And he went in to tarry with them.
Luk 24:30 And it came to pass, as he sat at meat with them, he took bread, and blessed it, and brake, and gave to them.
Luk 24:31 And their eyes were opened, and they knew him; and he vanished out of their sight.
Luk 24:32 And they said one to another, Did not our heart burn within us, while he talked with us by the way, and while he opened to us the scriptures?
Luk 24:33 And they rose up the same hour, and returned to Jerusalem, and found the eleven gathered together, and them that were with them,
Luk 24:34 Saying, The Lord is risen indeed, and hath appeared to Simon.
Luk 24:35 And they told what things were done in the way, and how he was known of them in breaking of bread.