Why do we not follow the rules or commandments of the Old Testament but continue to keep teaching the prophecy of the Old Testament? Why didn't the Old Testament prophecy get nailed to the cross too? Thanks.
"And you, being dead in your trespasses and the uncircumcision of your flesh, He has made alive together with Him, having forgiven you all trespasses, having wiped out the handwriting of requirements that was against us, which was contrary to us. And He has taken it out of the way, having nailed it to the cross" (Colossians 2:13-14).
"For He Himself is our peace, who has made both one, and has broken down the middle wall of separation, having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity" (Ephesians 2:14-16).
"Not that we are sufficient of ourselves to think of anything as being from ourselves, but our sufficiency is from God, who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life. But if the ministry of death, written and engraved on stones, was glorious, so that the children of Israel could not look steadily at the face of Moses because of the glory of his countenance, which glory was passing away, how will the ministry of the Spirit not be more glorious? For if the ministry of condemnation had glory, the ministry of righteousness exceeds much more in glory. For even what was made glorious had no glory in this respect, because of the glory that excels. For if what is passing away was glorious, what remains is much more glorious" (II Corinthians 3:5-11).
"But now He has obtained a more excellent ministry, inasmuch as He is also Mediator of a better covenant, which was established on better promises. For if that first covenant had been faultless, then no place would have been sought for a second. Because finding fault with them, He says: "Behold, the days are coming, says the LORD, when I will make a new covenant with the house of Israel and with the house of Judah -- not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they did not continue in My covenant, and I disregarded them, says the LORD. For this is the covenant that I will make with the house of Israel after those days, says the LORD: I will put My laws in their mind and write them on their hearts; and I will be their God, and they shall be My people. None of them shall teach his neighbor, and none his brother, saying, 'Know the LORD,' for all shall know Me, from the least of them to the greatest of them. For I will be merciful to their unrighteousness, and their sins and their lawless deeds I will remember no more." In that He says, "A new covenant," He has made the first obsolete. Now what is becoming obsolete and growing old is ready to vanish away" (Hebrews 8:6-13).
"Therefore, my brethren, you also have become dead to the law through the body of Christ, that you may be married to another--to Him who was raised from the dead, that we should bear fruit to God" (Romans 7:4).
The reason we speak of the ending of the Old Testament, or covenant or law, is because that is what God said would be replaced with a new set of law or covenant.
However, just because the covenant changed, it does not mean the Old Covenant became entirely useless.
"For whatever things were written before were written for our learning, that we through the patience and comfort of the Scriptures might have hope" (Romans 15:4).
"Now all these things happened to them as examples, and they were written for our admonition, upon whom the ends of the ages have come" (I Corinthians 10:11).
Concerning the prophecies of the Old Testament, much of what was written concerned the Messiah and the establishment of his kingdom. "To them it was revealed that, not to themselves, but to us they were ministering the things which now have been reported to you through those who have preached the gospel to you by the Holy Spirit sent from heaven -- things which angels desire to look into" (I Peter 1:12). The prophecies given in the Old Testament, fulfilled in the New Testament, become a solid testimony to the promises of God.
"And we desire that each one of you show the same diligence to the full assurance of hope until the end, that you do not become sluggish, but imitate those who through faith and patience inherit the promises. For when God made a promise to Abraham, because He could swear by no one greater, He swore by Himself, saying, "Surely blessing I will bless you, and multiplying I will multiply you." And so, after he had patiently endured, he obtained the promise. For men indeed swear by the greater, and an oath for confirmation is for them an end of all dispute. Thus God, determining to show more abundantly to the heirs of promise the immutability of His counsel, confirmed it by an oath, that by two immutable things, in which it is impossible for God to lie, we might have strong consolation, who have fled for refuge to lay hold of the hope set before us. This hope we have as an anchor of the soul, both sure and steadfast, and which enters the Presence behind the veil, where the forerunner has entered for us, even Jesus, having become High Priest forever according to the order of Melchizedek" (Hebrews 6:11-20).
The prophecies and promises of the Old Testament prove that God always keeps His word.