According to critics of the King James Version of the Bible the italicized words were not inspired and therefore should be left out of the text. Italicized words were added by the King James translators for easier reading in English when a literal translation could not be rendered.
But if the italicized words are not the words of God then why are they quoted by Jesus and many of the apostles?
We will first read the Old Testament verse, and then we will read the New Testament verse that quotes the Old Testament’s italicized words.
Note: The italicized words are in brackets
Moreover he said, I [am] the God of thy father, the God of Abraham, the God of Isaac, and the God of Jacob. And Moses hid his face; for he was afraid to look upon God. (Exodus 3:6)
I am the God of Abraham, and the God of Isaac, and the God of Jacob? God is not the God of the dead, but of the living. (Mat. 22:32)
And he humbled thee, and suffered thee to hunger, and fed thee with manna, which thou knewest not, neither did thy fathers know; that he might make thee know that man doth not live by bread only, but by every [word] that proceedeth out of the mouth of the LORD doth man live. (Deu. 8:3)
But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God. (Mat. 4:4)
Thou shalt not muzzle the ox when he treadeth out [the corn]. (Deu. 25:4)
For it is written in the law of Moses, Thou shalt not muzzle the mouth of the ox that treadeth out the corn. Doth God take care for oxen? (I Cor. 9:9. Also see I Tim. 5:18)
But the word [is] very nigh unto thee, in thy mouth, and in thy heart, that thou mayest do it. (Deut. 30:14)
But what saith it? The word is nigh thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach; (Romans 10:8)
I have set the LORD always before me: because [he is] at my right hand, I shall not be moved. (Psalm 16:8)
For David speaketh concerning him, I foresaw the Lord always before my face, for he is on my right hand, that I should not be moved: (Acts 2:25)
I have said, Ye [are] gods; and all of you [are] children of the most High. (Psalm 82:6)
Jesus answered them, Is it not written in your law, I said, Ye are gods? (John 10:34)
The stone [which] the builders refused is become the head stone of the corner. (Psalm 118:22)
Jesus saith unto them, Did ye never read in the scriptures, The stone which the builders rejected, the same is become the head of the corner: this is the Lord’s doing, and it is marvellous in our eyes? (Mat. 21:42)
This is the Lord’s doing; it [is] marvellous in our eyes. (Psalm 118:23)
Jesus saith unto them, Did ye never read in the scriptures, The stone which the builders rejected, the same is become the head of the corner: this is the Lord’s doing, and it is marvellous in our eyes? (Mat. 21:42)
Therefore thus saith the Lord GOD, Behold, I lay in Zion for a foundation a stone, a tried stone, a precious corner [stone], a sure foundation: he that believeth shall not make haste. (Isa. 28:16)
Wherefore also it is contained in the scripture, Behold, I lay in Sion a chief corner stone, elect, precious: and he that believeth on him shall not be confounded. (I Pet. 2:6)
In some cases the italics avoid what would otherwise be contradictions. For example 2 Samuel 21:19 says:
And there was again a battle in Gob with the Philistines, where Elhanan the son of Jaare-oregim, a Beth-lehemite, slew [the brother of] Goliath the Gittite, the staff of whose spear was like a weaver’s beam.
Without the italics Elhanan would be credited with having slain Goliath, rather than David. And 1 Chronicles 20:5 confirms that the italics in 2 Samuel 21:19 are correct, and reads:
And there was war again with the Philistines; and Elhanan the son of Jair slew Lahmi the brother of Goliath the Gittite, whose spear staff was like a weaver’s beam.
Because the New Testament writers quote Old Testament italics, this means that those italics were in the original manuscripts. Although the King James translators did not have those words in the Hebrew, they were lead by the Holy Spirit to put in the right words that are quoted in the Greek New Testament.
The italicized words are inspired.