There are several aspects and ways to view Malachi 3:3 which refers to the sons of Levi giving an offering in righteousness. As mentioned in a previous post, the priests were offering up sick and lame animals to Jehovah. The first instance in the scriptures that we are aware of an unacceptable offering is that of Cain in the Old Testament. The Prophet Joseph Smith had this to say about Cain and Abel's offerings to the Lord:
By faith in this atonement or plan of redemption, Abel offered to God a sacrifice that was accepted, which was the firstlings of the flock. Cain offered of the fruit of the ground, and was not accepted, because he could not do it in faith, he could have no faith, or could not exercise faith contrary to the plan of heaven. It must be shedding the blood of the Only Begotten to atone for man; for this was the plan of redemption; and without the shedding of blood was no remission; and as the sacrifice was instituted for a type, by which man was to discern the great Sacrifice which God had prepared; to offer a sacrifice contrary to that, no faith could be exercised, because redemption was not purchased in that way, nor the power of atonement instituted after that order; consequently Cain could have no faith; and whatsoever is not of faith, is sin. But Abel offered an acceptable sacrifice, by which he obtained witness that he was righteous, God Himself testifying of his gifts. Certainly, the shedding of the blood of a beast could be beneficial to no man, except it was done in imitation, or as a type, or explanation of what was to be offered through the gift of God Himself; and this performance done with an eye looking forward in faith on the power of that great Sacrifice for a remission of sins. But however various may have been, and may be at the present time, the opinions of men respecting the conduct of Abel, and the knowledge which he had on the subject of atonement, it is evident in our minds, that he was instructed more fully in the plan than what the Bible speaks of, for how could he offer a sacrifice in faith, looking to God for a remission of his sins in the power of the great atonement, without having been previously instructed in that plan? And further, if he was accepted of God, what were the ordinances performed further than the offering of the firstlings of the flock? (Joseph Smith, Teachings of the Prophet Joseph Smith, selected and arranged by Joseph Fielding Smith, p.58)
Here the Prophet teaches that an acceptable sacrifice or offering in righteousness must be done in faith, looking to Christ and his atonement. According to Oliver Cowdery and his recollection of the appearance of John the Baptist, the wording of John's message was as follows, "Upon you my fellow-servants, in the name of Messiah, I confer this Priesthood and this authority, which shall remain upon earth, that the Sons of Levi may yet offer an offering unto the Lord in righteousness!" (emphasis added)
Joseph Smith History - Oliver Cowdery Footnote (JS - History)
The space above the ancient temple altar was considered sacred and was viewed as a conduit that went straight into heaven. After Solomon's Temple was dedicated, Israel prayed facing the temple as if their prayers traversed the land until they arrived at the temple altar and there they would ascend to heaven as an acceptable offering. That concept may be viewed even today as all covenants in the temple are made at an altar including marriage. These covenants are an offering in righteousness to the Lord. Omni 1:26, we learn that we are to offer up our whole souls to God. Both our whole souls and our marriages are offered to the Lord at the sacred altars.
Isaiah suggests that latter-day converts to Christ are to be brought to the temple as an offering to the Lord.
20 And they shall bring all your brethren [for] an offering unto the LORD out of all nations upon horses, and in chariots, and in litters, and upon mules, and upon swift beasts, to my holy mountain Jerusalem, saith the LORD, as the children of Israel bring an offering in a clean vessel into the house of the LORD. (emphasis added)
Finally, in the Doctrine and Covenants section 128 the Prophet teaches that we are to bring the names of our dead ancestors to the temple as an offering in righteousness,
24 Behold, the great day of the Lord is at hand; and who can abide the day of his coming, and who can stand when he appeareth? For he is like a refiner's fire, and like fuller's soap; and he shall sit as a refiner and purifier of silver, and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness. Let us, therefore, as a church and a people, and as Latter-day Saints, offer unto the Lord an offering in righteousness; and let us present in his holy temple, when it is finished, a book containing the records of our dead, which shall be worthy of all acceptation. (emphasis added)
From the above, we can see that there are at least four major offerings in righteousness that each of us can make in the temple of God: 1. our whole souls 2. our converts to Christ 3. our ancestors who have passed on and 4. our marriages. Thus we fulfill the Lord's commands that he requires the heart and a willing mind (D&C 64:34).
Each covenant member of the Church along with their converts and dead ancestors are brought to the altars of the temple where each can offer up their whole souls to God with a commitment to establish his righteousness on the earth (D&C 1:16).