It helps to consider the word "house" in I Peter 2:5 meaning something a bit different from the common definition. Most commonly, we think of a building people live in. Here, "house" can just as easily mean "dynasty," as in the "house of David."
God is building us up into a dynasty, a spiritual house, a spiritual Family, one that we know will last forever. Verse 5 adds that God is forming us into a holy priesthood, the purpose of which is to offer up acceptable spiritual sacrifices to God through Christ. Verse 9 confirms that we are already a royal priesthood. This is especially important in light of the sacrifices, because those sacrifices were the activity of the priesthood under the Old Covenant.
Those priests went through the entire ritual physically. God does not require us to follow those procedures, yet He does require us to understand the spiritual concepts and apply them to the best of our ability. Why? Because we are being built up into a spiritual Family whose function is to glorify God by offering spiritual sacrifices that He will accept.
We must not allow ourselves the liberty of detaching ourselves from this by saying, "Well, that is really interesting information and nice to have, but of what value is it?" It is of great value, as the prophet Malachi clearly shows. In Malachi 1:6, God chastises the priesthood for the irresponsible manner in which they were carrying out their charge from God: "'A son honors his father, and a servant his master. If then I am the Father, where is My honor? And if I am a Master, where is My reverence?' says the LORD of hosts to you priests who despise My name." Those are strong words for failing to offer sacrifices pleasing to God.
The priesthood may not have come to a deliberately reasoned conclusion that the worship of God was something unimportant, but their inner disrespect surfaced in their slipshod and lackadaisical approach. God says He looks on the heart (I Samuel 16:7), and His evaluation of their performance is that they considered their responsibility of offering sacrifices to Him to be shameful. Their real problem lay in their heart. Distracted by concerns they considered more important, their goal of being a whole burnt offering dedicated to God became a secondary occupation for their attention and energy.
The focus of their attention may easily have been given to functions and duties considered normal, everyday concerns, not sin per se. Nevertheless, these things are of lesser importance than fulfilling their charge from God. They reply to God in a manner that can be interpreted as offended surprise, asking, "In what way have we despised Your name?" God replies that the food they offered on His altar was defiled (Malachi 1:7).
Recall that a basic feature of the offerings is of God eating a meal. The altar is His table, and the sacrifice is His food. The fire consuming the offerings pictures God devouring it. As a result of "eating" the meal, He is satisfied just as we would feel a sense of well-being following a fine meal. God, however, is not satisfied with the sacrificial "meals" the priests of Malachi's day offered; He complains of their poor quality. They give Him no satisfaction and are not acceptable.
The quality of their offerings had become so poor as to be downright evil. The priests would never have served such blemished beasts to a leader they could see, but they gave them to the invisible God. Their faith was so weak that He was not only out of sight, He was almost completely out of mind (Psalm 10:4)! They had no thought of the greatness of His power; His merciful, loving providence; the desire of His concern for their well-being; or of His nearness to them. They apparently never gave it much thought that He was aware of all they were doing!
King David was cut from an entirely different bolt of cloth. The books of Samuel, Kings, and Chronicles clearly portray the external flaws in his behavior. We see his lust and adultery, his scheming deceit in conspiring to have Uriah die in battle, his childrearing errors, and his mistakes within the intrigues of government.
Like us, David was encompassed with human nature. In principle, we do many of the same things as he did, and also like him, it is an ever-present reality. It can break out at any time we get far from God and let our defenses down. However, in the Psalms we receive insight into his heart. In them, we see the real man, the one after God's own heart, and this forms the basis of God's judgment of him.
Malachi teaches us that we must strive to offer to God the best we can. Not everybody is the same. Each of us has our own package of abilities, intelligence levels, and skills. We have different attitudes about things and circumstances. We have been reared in different kinds of environments, and so our attitudes toward things are not always the same. We have different sins and weaknesses to overcome.
On the one hand, the ideals of the offerings are shown in the life of Jesus Christ, but on the other is the reality of what we are. We do not come anywhere near the ideals; we are frequently unstable and inconsistent. God nonetheless wants the general trajectory of our lives to be consistently aimed toward achieving them.
We all have our peaks and valleys. God is not overly concerned about the occasional valleys we go through as long as we are consistently bouncing back, making strenuous effort to bring the very best offering we possibly can into God's service. This approach will work to produce the maturity God desires to see in us; the image of Jesus Christ will be formed. This attitude will produce the satisfaction in God and us that is the fruit of the peace offering.