Convenant is a solemn agreement amongst poeple or between God and His people (man) involving commitment and guarantees. The role that convenant played in the Historical Salvation is that as time passed the poeple will always have the convenant to remember there by making their promises to stand. When they stray from God the convenant will rind God of His own promise to them therefore making Him to forgive their sins.
As time goes by the convenant gets stronger and so will keep the people together with God.