Indeed, at first Jesus seems to be simply passing on a known lesson in good manners, such as can be found in Proverbs 25:6-7. However, the motive of both types of dinner guests is suspect and comes from selfish interests, since a "higher position at table" is being sought by the crafty device of pretending humility. Jesus knows the hearers would rebel at this; after all, he is in the house of a Pharisee in the company of other Pharisees who are known to all for their self-seeking behaviour in pursuit of conspicuous honour, in a culture where "honour" is everything.
Then Jesus puts the shoe on the other foot (so to speak). The really honourable thing to do, he says, is to invite those who can’t play "back scratch," with those who can’t reciprocate. That means inviting the poor, the sick, the lame, and the needy. But by doing that in such a culture you dishonour yourself because you have gone outside your social status level and you would be publicly humiliated.
This is precisely Jesus' point and message, and the challenge of the parable. He is saying that no one must be excluded from the gathering at the community banquet. Only God can determine who is to be honoured - as indeed God will do on the day of resurrection, paying special honour to those who invited the uninvitable.
The problem facing Luke's community, perhaps fifty years after the Ascension, is simply "how to treat the poor at the Eucharistic meal." The answer is clear, based on this parable of Jesus no one is to be excluded from the Eucharistic meal based on social status. Barriers to covenant love must come down -- no rich, no poor, no Jew, no Gentile. Christians are to be one humble family, united. Only God determines honour, based on the way we humbly treat each other.
True humility brings us back into the light of communion between the Father and his Son Jesus Christ and with one another; for this reason asking forgiveness for creating barriers to unity is a prerequisite for both the Eucharistic liturgy and personal prayer. Our total dependence on God is called poverty of spirit and prepares us for the kingdom.