For whatever things were written before were written for our learning, that we through the patience (perseverance) and comfort of the Scriptures might have hope.”  Romans 15:4

The whole Bible is the revelation of Jesus Christ.  
As an aside; somewhere and forgive me I can’t remember where, I read this overview of the Bible:
   In the Old Testament Jesus is expected.
   In the Gospels Jesus is revealed.
   In the Acts Jesus is preached.
   In the Epistles Jesus is explained.
   In the Book of Revelation Jesus is anticipated.

“But as it is written; 
‘Eye has not seen, nor ear heard,
Nor have entered the heart of man 
The  things which 
God has prepared for those who love Him.’
But God has revealed them to us through His Spirit…Even so no one knows the things of God except the Spirit of God.”  1 Corinthians 2:9-11

As we continue looking into the written word, we turn to Psalm 19 to see several propositions set forth that have been tested and proven down through the ages.  That is; the written word of God is perfect, sure, right, pure, enduring, true and righteous.  Those who belong to Christ today join the saints of old in joyous agreement.  

Psalm 19:
“The testimony of the LORD is sure , making wise the simple”  Vs:7
“So the law is holy, and the commandment is holy and righteous and good.”  Romans 7:12
“Repent therefore, and turn back, that your sins may be blotted out.”  Acts 3:19

“The testimony of the LORD is sure, making wise the simple”  Vs:7
“And because of Him you are in Christ Jesus, who became to us wisdom from God, righteous and sanctification and redemption.”  1 Corinthians 1:30

“The statutes of the LORD are right, rejoicing the heart”  Vs:8
“…for the ways of the LORD are right, and the upright walk in them...”  Hosea 14:9

“The commandment of the LORD is pure, enlightening the eyes”  Vs.8
“every word of God proves true; He is a shield to those who take refuge in Him.”  Proverbs 30:5
“For God who said, ‘Let light shine out of darkness,’ has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ.”  2 Corinthians 4:6

“The fear of the Lord is clean, enduring forever”  Vs.9
“…Fear God and keep His commandments, for this is the whole duty of man.”  
Ecclesiastes 12:13

“The judgments of the LORD are true and righteous altogether.”  Vs.9
“The sum of Your word is truth, and every one of Your righteous rules endures forever.”  
Psalm 119:160

The Bible is a whole unit, therefore man dare not choose the parts he wants to believe and dismiss the rest. To those who would say that the Old Testament has no relevance today, I given the following Scripture:
 
Jesus speaking to the two on the Emmaus road:
“Then He said to them, ‘These are My words that I spoke to you while I was still with you, that everything that is written about Me in the Law of Moses and the Prophets and the Psalms must be fulfilled.”  Luke 24:44

“He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son.  And this is the testimony: that God has given us eternal life, and this life is in His Son.”  
1 John 5:10-11

May the Holy Spirit reveal the truth of the Word to those loved ones who are still walking in darkness.   Amen