Let's observe Mark 16:16. He that believes and is baptized shall be saved. That is a promise to those who believe and obey the voice of God it also is a promise to dam those who don't believe.
Those who believes enters into the promise as to say, they covenant with God in obeying the voice of God , it is no longer just a promise it is the fulfillment of the promise through the actions of the believer.
On the other hand, those who reject the word of God will be dammed because of unbelief refusing to value and trust the word of God. Promises of God are Yea and AMEN! When you embrace and enter the promises, they become covenants.