We don't "enter" any "covenant". We are partakers of Christ BY THE GOSPEL!
We enter the covenant by believing and obeying.
Paul is the minister of the covenant.
Here Paul tells when Jesus made that covenant:
1 Corinthians 11:25 In the same way,
after supper He took the cup, saying, "This cup is the new covenant in My blood; do this, as often as you drink it, in remembrance of Me."
Here Paul tells how Jesus gave the covenant that was promised a long time ago when God said He would write the new law on our hearts:
2 Corinthians 3:3 It is clear that you are a letter from Christ, the result of our ministry,
written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts.
Paul is explaining that HE COULD NOT CHANGE THE COVENANT, which further proves Paul taught exactly what Jesus taught when he walked the earth:
Galatians 3:15 Brothers, let me put this in human terms.
Even a human covenant, once it is ratified, cannot be canceled or amended.
When Jesus was on earth, he made the testament/covenant conditions, and then he died for the testament and covenant, rose again, and ascended.
Jesus couldn't come and make a different gospel/covenant with Paul because this is the one and only everlasting covenant of his blood.
Hebrews 13:20 Now may the God of peace,
who through the blood of the eternal covenant brought back from the dead our Lord Jesus, the great Shepherd of the sheep,
Covenants must be followed exactly. Last wills and testaments must be followed exactly. Last wills and testaments tell us who gets in the will and what they will get.
Jesus walked the earth and he gave the conditions to enter the covenant. Jesus walked the earth and he gave the conditions to for his Last Will and Testament.
Paul didn't give another gospel/testament/covenant! He was a minister of the same one and only covenant that Jesus made with his blood.