New Revised Standard Version
and say to him, Take heed, be quiet, do not fear, and do not let your heart be faint because of these two smoldering stumps of firebrands, because of the fierce anger of Rezin and Aram and the son of Remaliah.

Contemporary English Version
Tell Ahaz to stop worrying. There's no need for him to be afraid of King Rezin and King Pekah. They are very angry, but they are nothing more than a dying fire. Ahaz doesn't need to fear

New American Bible
and say to him: Take care you remain calm and do not fear; do not let your courage fail before these two stumps of smoldering brands, the blazing anger of Rezin and the Arameans and of the son of Remaliah—

Douay-Rheims Bible
And thou shalt say to him: See thou be quiet: fear not, and let not thy heart be afraid of the two tails of these firebrands, smoking with the wrath of the fury of Rasin king of Syria, and of the son of Romelia.

And thou shalt say to him: See thou be quiet: fear not, and let not thy heart be afraid of the two tails of these firebrands, smoking with the wrath of the fury of Rasin king of Syria, and of the son of Romelia.

take heed

Isaiah 30:7,15 For Egypt shall help in vain, and to no purpose: therefore have I cried concerning this: It is pride only, sit still. . . .

Exodus 14:13,14 And Moses said to the people: Fear not: stand, and see the great wonders of the Lord, which he will do this day; for the Egyptians, whom you see now, you shall see no more for ever. . . .

2 Chronicles 20:17 It shall not be you that shall fight, but only stand with confidence, and you shall see the help of the Lord over you, O Juda, and Jerusalem: fear ye not, nor be you dismayed: to morrow you shall go out against them, and the Lord will be with you.

Lamentations 3:26 Teth. It is good to wait with silence for the salvation of God.

fear not

Isaiah 8:11-14 For thus saith the Lord to me: As he hath taught me, with a strong arm, that I should not walk in the way of this people, saying: . . .

Isaiah 35:4 Say to the fainthearted: Take courage, and fear not: behold your God will bring the revenge of recompense: God himself will come and will save you.

Isaiah 41:14 Fear not, thou worm of Jacob, you that are dead of Israel: I have helped thee, saith the Lord: and thy Redeemer the Holy One of Israel.

Isaiah 51:12,13 I myself will comfort you: who art thou, that thou shouldst be afraid of a mortal man, and of the son of man, who shall wither away like grass? . . .

Matthew 10:28 And fear ye not them that kill the body, and are not able to kill the soul: but rather fear him that can destroy both soul and body in hell.

Matthew 24:6 And you shall hear of wars and rumours of wars. See that ye be not troubled. For these things must come to pass: but the end is not yet.

neither be faint-hearted.

Deuteronomy 20:3 Hear, O Israel, you join battle this day against your enemies, let not your heart be dismayed, be not afraid, do not give back, fear ye them not:

1 Samuel 17:32 And when he was brought to Saul, he said to him. Let not any man's heart be dismayed in him: I thy servant will go, and will fight against the Philistine.

the two tails

Isaiah 7:8 But the head of Syria is Damascus, and the head of Damascus is Rasin: and within threescore and five years, Ephraim shall cease to be a people:

Isaiah 8:4 For before the child know to call his father and his mother, the strength of Damascus, and the spoils of Samaria shall be taken away before the king of the Assyrians.

2 Kings 15:29,30 In the days of Phacee, king of Israel, came Theglathphalasar, king of Assyria, and took Aion, and Abel Domum Maacha, and Janoe, and Cedes, and Asor, and Galaad, and Galilee, and all the land of Nephthali: and carried them captives into Assyria. . . .

Amos 4:11 I destroyed some of you, as God destroyed Sodom and Gomorrha, and you were as a firebrand plucked out of the burning: yet you returned not to me, saith the Lord.