In Romans 10:9–10 Paul writes:
"that if you confess with your mouth 'Jesus is Lord' and believe with your heart that God raised him from the dead, you will be saved; because with heart one believes to righteousness and with mouth one confesses to salvation."
We understand from this that it is essential that believing with one's heart that God raised Jesus from the dead, is accompanied by confessing with one's mouth that Jesus is Lord.
The confessions in 1 Cor 15:3b–7 and 1 Tim 3:16 are longer than the very short one:
Jesus is Lord
given above in Rom 10:9 and given also for example in 1 Cor 12:3.
Another confession, equally short, is the one:
Jesus is Christ
referred to in for example John 9:22 and 1 John 5:1.
We will in the following argue that these two short confessions are implied by both 1 Cor 15:3b–7 and 1 Tim 3:16.
Reading the speech of Peter at the day of Pentecost (Acts 2:14–36), one sees that Peter there holds forth the following facts:
From the above Peter concludes that God had made Jesus both Lord and Christ:
"Therefore, let all the house of Israel know for sure that God made him both Lord and Christ, this Jesus whom you crucified." (Acts 2:36)
And on the day of pentecost 3000 were convinced by the message of Peter and were baptized (Acts 2:41).
The confessions in 1 Cor 15:3b–7 and in 1 Tim 3:16 have a content which corresponds to most of the above points in the speech of Peter. These similarities and Peter's conclusion in Acts 2:36 suggest that both 1 Cor 15:3b–7 and 1 Tim 3:16 are an indirect manner of confessing:
Jesus is Lord and Jesus is Christ.
Similar to the speech of Peter, also these confessions provide evidence that God has appointed Jesus to the titles Lord and Christ by resurrecting him from the dead, and therefore that these titles rightfully belong to him.
Further, from Paul's introduction to the confession in 1 Tim 3:16, we understand that it was usual for the believers in Ephesus – where Timothy stayed at the time of Paul writing this letter to him – to orally say or sing this confession.
From 1 Cor 15:1–3 and 11 we understand that Paul had delivered the confession in 1 Cor 15:3b–7 orally, and it is not unreasonable that many of the Corintians would have learned this confession by heart and could orally deliver it further.
In Paul's introduction to the confession in 1 Cor 15:3b–7 he calls it the gospel. We therefore understand that believers could use both this confession and the one in 1 Tim 3:16 as a summing-up of the gospel of Christ to remind oneself and each other of what they had learned orally from the apostles about the Lord Jesus Christ. They also could actively use such confessions when further spreading the gospel. It may be helpful to use these confessions for similar purposes today. They may especially be helpful in places where the gospel is not known or there is a shortage of Bibles.
However, to orally speak out the fundamentals of one's belief may be helpful in many circumstances, also when no shortage of Bibles.
Personally, I have experienced to receive help from these confessions, not only by the mental process of speaking them, but also by the thought flow in these two confessions. Especially, when taken together, I find the thought flow in these confessions very convincing. Many times, having been discouraged by different circumstances, these confessions have encouraged me to focus on that Jesus was really raised and seen by eyewitnesses. I then know for sure that God made Jesus both Lord and Christ with all the glorious consequences thereof.