What is an “altar offering”? Should we give it separately from the usual offering on Sunday? Is it biblical?

I may be wrong, but I am guessing you are referring to Matthew 5:24 in which Jesus is talking to Jewish people.  He says to these Jewish people that if they are presenting a gift at an altar, but have an unresolved problem with a brother or sister, they should take care of a problem with a brother or sister first, before making the offering.  Well, we need to look at the context.  Jesus is talking to Jewish people, for whom presenting gifts at an altar (such as the burnt offering, or the grain offering or a fellowship offering) was a part of normal worship.  This is why Jesus used this example (including an altar) for his Jewish audience.  We Christians do not present burnt offerings or grain offerings, and we do not have altars.  However, we need to look at what Jesus was teaching.  The principle applies to us for sure, even if the part about the altar does not.  If we are worshipping God (for example if we are at church or if we are taking the Lord’s Supper) but we have a problem with a brother or sister, we need to make dealing with the issue a priority–perhaps even doing that before we come to worship God.  The altar, in this case, does not apply to us, as we are not Jews, but the concept certainly does.  Let us not allow disagreements or sins against a fellow believer fester, but let us deal with such issues quickly, so that it does not hinder our or other peoples’ worship of God.  That is the principle.

Now, I may be off here, and you are not referring to Matthew 5:24.  Let me know if that is the case, and if I have not answered your question adequately.

John Oakes