Christ declares the Decree of the Lord in Psalm 2:7, starting by confessing His IDENTITY - His SONSHIP, as the Firstborn from the dead. Then in v8, He continued to declare what God said to Him at His Resurrection-Ascension: "Ask of Me, and I will give You (1) the nations for Your inheritance, and (2) the ends of the earth for Your possession." The spiritual warfare between the Kingdom of God and the kingdom of darkness is over (1) the souls of men (the nations), and (2) the control of the earth itself. With His Blood, Jesus redeemed (purchased) both (1) the the souls of men, and (2) the earth (Revelation 5), which is why He alone has the right to open the Scroll with 7 seals (the Title Deed of the earth). Psalm 2:8 should be translated: "Ask of Me, and I will give You (1) the nations - Your inheritance, and (2) the ends of the earth - Your possession." Thus the nations are already Christ's inheritance and the earth is already His legal possession. But there is a difference between possessing something legally and experientially - for example God gave Israel the Promised Land legally through Abraham (Joshua 1:3), and then later experientially through Joshua (Joshua 1:2). So having just granted Him the inheritance that He had purchased with His Blood, and having ordained and anointed Christ as the great heavenly High Priest (Psalm 110:4), the Father told Him to ask of Him, and He would hand over to Him the souls that belong to Him (John 6:37). Since then Christ ever lives to make intercession for us at God's right-hand (Hebrews 7:25, Romans 8:34), releasing the Holy Spirit to convict us, regenerate, save and sanctify us to Himself - we are His inheritance (Ephesians 1:18). If we are saved, it is only because Christ prayed for us, and asked the Father to give us to Him.
In Christ, we are also anointed to be royal priests in the order of Melchizedek (Psalm 110:3-4, Revelation 1:6, 5:10, 1Peter 2:9), and so we are to share in His ministry of intercession by the power of the Spirit, especially in praying for the Holy Spirit to fill us and empower us to reach the lost, and for Him to soften their hearts and open their eyes, so they might receive Christ. In other words, v8 also applies to us - we are to ask God to save people by His Holy Spirit and cause them to grow spiritually, so that they become our inheritance (the fruit of our ministry). Christ must have taught the apostles this truth from Psalm 2 during the 40 days, because in Acts 4:23-31 we see them using Psalm 2 as the basis for their prayers to be filled with the Spirit to preach the Gospel, for the salvation of the lost, resulting in a harvest of souls (Acts 4:33, 5:12-16). In addition, the Father told Christ to ask Him to give Him actual possession of the earth. This is when He moves into action as the anointed King - he is worthy to be the Lion-King, because He was the sacrificial Lamb of God (Revelation 5). This will be start to be fulfilled in the Day of the Lord (Tribulation), when Christ no longer sits, but stands and starts to make His enemies His footstool, by moving in judgment (Psalm 110:1, Revelation 5:6). At the 2nd Coming, Christ will complete His judgments against His enemies, and take full possession of the earth and establish His Kingdom here, ruling the world with a rod of iron, in fulfilment of Psalm 2:9: "You shall break them with a rod of iron; you shall dash them to pieces like a potter’s vessel.” At the 2nd Coming, He will be manifested as God's ordained and anointed King of kings, ruling over His Kingdom with a rod of iron (Revelation 19:15-16, 12:5), and in Christ we will also be anointed kings, who share in His rulership (Revelation 2:26-27). Thus v8-9 also applies to us, which means that in our present spiritual warfare, in fulfilling our mission on earth, we are to use His rod of iron (the Name of Jesus) to break the power of the enemy, when it comes against us, and in setting the captives free.