Matthew Chapter 5

"23 Therefore if you bring your gift to the altar, and there remember that your brother has something against you, 24 leave your gift there before the altar, and go your way. First be reconciled to your brother, and then come and offer your gift. "

We can assume from this verse that God will not be pleased with the gift unless we are reconciled with our brethren first. Therefore, if we are holding grudges with our brethren and do not make peace with them, then God will probably not accept our gift. In the same way, if we are unable to love our brethren and live harmoniously with them, God will probably not listen to our offers of prayer (the spiritual incense).

Furthermore, here it mentions that "your brother has something against you", which could be that you do not have something against your brother. Even then, God wants us to reconcile with that person who has something against us even if we have nothing against them. If we know there's something wrong, even if we don't have bad feelings, it is our duty to dissolve the bad feeling with the other person. Many times, these bad feelings result from misunderstandings between brethrens. If everyone can put themselves in other people's shoes before making comments and judgments, I think it would easier to keep harmony between brethrens.

Therefore, even if we do not hold a grudge against our brethren but know that someone has something against us, God will still hold us accountable to make peace before He will accept us.