In Heb 11:4, we read:
By faith Abel offered
unto God a more excellent sacrifice than Cain, by which he obtained witness
that was righteous, God testifying of his gifts: and by it he being dead yet
speaketh.
The term "righteous" is δικαιος; it is clear that God accepted the offering of Abel, not because Abel was the recipient of an alien righteousness, but due to the intrinsic righteousness Abel demonstrated with his sacrifice as opposed to Cain. However, such was not based on strict, legal merit, but God’s gracious merit. As we read in Gen 4:4-5:
And Abel, he also brought of the firstlings of the flock and the fat thereof. And the Lord had respect unto Abel and to his offering. But unto Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell.
It was due to the (covenantal) relationship between Abel and God that God accepted the offering and such was a demonstration of Abel being truly, not declaratively merely, righteous.
I bring this up as the following verse, addressed to Vinson Knight, brings up the topic of offering to God something that the Lord will accept due to the covenantal relationship between God and man:
And let him lift up his voice long and loud, in the midst of the people, to plead the cause of the poor and the needy; and let him not fail, neither let his heart faint; and I will accept of his offerings, for they shall not be unto me as the offerings of Cain, for he shall be mine, saith the Lord. (D&C 124:75)
Notice that it is not the nature of the offering per se in this verse, but the determining factor is whether one is faithful to their covenantal relationship with God. If we abide in the covenant, God will reward us, again, not on the basis of strict legal merit, but gracious merit.