A covenant is an agreement between two parties. In some cases, the parties stand on equal footing, and each party contributes to the conditions of the covenant.
It can be the case, however, that one of the parties is infinitely superior to the other, as in the case of God versus man.
Accordingly, the superior (God) has the right to dictate the terms of the agreement solely. The Creator commands; we submit!
The Scriptures mention several covenants, such as God's covenant with Adam and Eve (Gen. 3:15-21) and the covenant with Noah (Gen. 6:13-22).
There are two major covenants of the Bible.
First, God made a covenant at Sinai with the Israelite nation (Ex. 20:1-24; cf. Dt. 5:1-5). This covenant was preparatory in nature and temporary in duration; it was abolished by the death of Christ (Rom. 7:4-6; 2 Cor. 3:1ff; Gal. 3:19, 24-25; Eph. 2:14ff; Col. 2:14ff; Heb. 8:7ff).
Second, Christ inaugurated a new covenant from Jerusalem (see Gal. 4:25), universal in scope (see "many" Mt. 26:28), that was ratified by the shedding of his blood, and is binding until the end of time (cf. Jer. 31:31-34; Heb. 9:15-17).
Men today, therefore, are not amenable to the Mosaic code with its animal sacrifices, physical priesthood, sabbath days, etc.