It is exciting to find the Gospel all throughout the Psalms. For example, Psalm 98 speaks of God remembering His lovingkindness to Israel by openly demonstrating His salvation in the sight of all nations and revealing His righteousness. This immediately reminds me of Romans 1:16-17 where we are told that the Gospel reveals the righteousness of God, being the power of God unto salvation to all who believe, to the Jew first and also to the Greek (i.e, Gentile). Now it might be said that Psalm 98 is referring to God saving Israel out of Egypt through Moses, or it may be referring to something that is more contemporary with the psalmist, but it is important to recognize that it is also prophetic, foreseeing the eschatological salvation accomplished by the Messiah and the subsequent worldwide judgment (98:9). God saving His people was also prophesied in Psalm 130:8, Isaiah 53:8, and Matthew 1:21. Although Israel in Psalm 98:3 most naturally refers to ethnic Israelites, the psalm also commands all the earth to rejoice in God's salvation. This is because the promise of blessing extends through Israel to all nations through the promise given Abraham, and this why Matthew starts his narrative by telling us that Jesus Christ was not only the son of David, but also the son of Abraham and purposefully includes at least two ethnic Gentile women in the genealogy account.
That Jesus was the long-awaited Christ, the Son of God, who saved His people from their sins is the Gospel message. We now know that "His people" includes both ethnic Israelites and ethnic Gentiles from every nation under heaven, just as was foreseen in Psalm 98. However, there is no way for us to deduce from the Gospel message itself that "Christ died for me" individually, unless of course, Christian Universalism be true and every one without exception be received into glory immediately upon death. Since Scripture obviously doesn't teach this, there must be some people for whom Christ did not die. Jesus plainly states this in John 8:47 and John 10:26 when He tells some of the Jews that the reason why they don't believe in Him is because they are not of God and not of His sheep. Therefore, no one who has not yet believed the Gospel can assure himself that Christ died for him individually. And none of the Apostles ever required anyone to believe such a thing. For them the Gospel message was simple: Jesus is the Christ, the Son of God. Every one who believes this has life in His name. The problem is that the bulk of churches today are oblivious to this message or else find it offensive and an insipid thing. It crushes their pride because it leaves them completely dependent on the sheer mercy of God, with no assurance of being one of His favorites and no way to procure such a status. In other words, this message can't be good news for them because it doesn't designate them individually and provides them no employment in the matter. Despite this, the message that Jesus is the Christ, the Son of God, who performed His saving act remains good news to those who can receive it. Again, this is why the author of Psalm 98 immediately commands all the earth to shout joyfully and sing for joy and sing praises. When good news is believed, it naturally gives the believer a reason to be joyful. And this is how people who initially appeared to be on the outside of this good news find themselves to be on the inside, namely by believing it and rejoicing in what God has done simply for the sake of what God has done. God has performed His righteous deed! Christ has given His people eternal life by rising from the dead! Hallelujah! This is how the emphasis remains on God's righteousness, rather than on the sinner appropriating righteousness to himself through some act, whether it be some mystical and elusive "heart work" that masquerades under the name of faith or whether it be some outward thing, such as repeating a prayer, walking an aisle, or undergoing a ritual like water baptism. In contrast to sinners attempting to appropriate righteousness to themselves, Christ's people partake of God's righteousness when they believe the bare report of what He has done (Psalm 22:31, Isaiah 53:1). By believing it, they come to reflect the glory of it as it shines upon them unto eternal life (Psalm 34:5, 36:9).