Compare this with I Peter 2:5 and 9 and the responsibility of the church: 1) to bring sacrifices acceptable to God by Jesus Christ and 2) to proclaim the praises of God.
Peter sees the church as part of the fulfillment of this prophecy—focusing on a people who will truly serve and glorify God in contrast to disobedient Israel. The church is a forerunner of what is to come. This also confirms, in a general way, that we have been formed for the purpose of proclaiming His praises, which is what a priest does! Thus, Peter writes that we are to offer up spiritual sacrifices acceptable to God by Jesus Christ.
This priesthood is not yet fully formed, but rather, it is one that is being formed. As such, we nonetheless are expected to perform certain functions in preparation for our formal installation that will not occur until Christ returns and establishes the Kingdom of God on earth. Then, that priesthood will appear suddenly, fully formed.
God has spent 6,000 years forming it. We are called to be kings and priests (Revelation 5:10). And even now Peter makes sure that we understand that we are already a priesthood—a priesthood in training. Yet, even though we are in training, we have priesthood responsibilities, for he says in verse 5 that we are—now, presently—to offer up spiritual sacrifices.
John W. Ritenbaugh
New Covenant Priesthood (Part 1)