ST IIIa, q. 53, art. 1). Here they are.
1. It reveals God’s justice. Because Christ humbled himself and died on the cross out of love and obedience to the Father, God lifted him up by a glorious resurrection.
2. It was necessary for the confirmation of our faith in Christ. Thomas cites Paul, who explains that the resurrection attests to the power of God (2 Cor 13:4).
3. It gives us hope for the resurrection of our bodies. This, of course, is the whole point of 1 Corinthians 15. As Paul writes, “Now if Christ be preached that He rose from the dead, how do some among you say, that there is no resurrection of the dead?" (1 Cor 15:12)
4. It means death to sin and new life in Christ for us. Since we are united with Christ we have not only died with him but been raised with him to newness of life. Thomas cites Romans 6:4, 11: “We were buried therefore with him by baptism into death, so that as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life… 11 So you also must consider yourselves dead to sin and alive to God in Christ Jesus.”
5. It completes the work of salvation. This is an especially important point that is far too often overlooked. Christ’s death is not the only aspect of his work for our salvation. Again, Thomas cites Paul, who explains that Christ was “put to death for our trespasses and raised for our justification” (Rom 4:25). Most people forget about this verse and simply profess that Jesus died for our salvation--but that's only part of it!
Notice that Thomas pays very close attention to Paul’s language in particular here.
Salvation involves two elements: (1) the payment of the debt due to sin, which is accomplished on the cross (e.g., he was “put to death for our trespasses”) and (2) he is raised for our sakes as well (e.g., "for our justification"). Ultimately, Jesus’ resurrection wasn’t for his sake but for ours. The goal of salvation was not simply to save us from sin, but to unite our humanity to God. Peter explains that we are called to become “partakers of the divine nature” (2 Pet 1:4).
Christ’s resurrection then is the cause of our sharing in the new life of grace―the unity of our humanity with divinity. Salvation isn’t just a matter of being delivered from the punishment due to sin, namely, hell―it also means being delivered to life in God (cf. also ST IIIa q. 56, art. 2; cf. also IIIa q. 57, art. 6.; also see the Catechism of the Catholic Church, paragraph 654).
Hallelujah―He is Risen!