It is hard to conceptualize Final Participation - not least because it is usually explained in terms of what it is not.
But just as Final Participation is the same thing as development of the individual person - but at the level of groups or societies - so Final Participation can be understood as what happens with an ideal marriage as the most mature form of human relationship.
The child is, to start with, in Original Participation - immersed in parental love and with his self not differentiated from this environment. Everything is conscious and alive in a delocalized, overlapping and undifferentiated way. He lives inside Love.
With maturation and especially adolescence, the child differentiates himself from this diffuse and unlocalized state. At some stage he reaches a point of inflexion when he is cut-off from love, loses all ties of relationship, and find himself a fully detached self, observing his environment - sometime the environment seems real and himself an illusion (positivism/ materialism), sometimes the opposite (solipsism). This adolescent phase of alienation may last a moment, or it may persist for the rest of his life (as - apparently - with so many modern people).
Marriage is (ideally) Final Participation: it is engaged objectivity. The spouse is seen not as a subject (about whom we can think whatever we choose, indifferent to the person), nor an object (to evaluate you spouse objectively - by checklist - is a failure of marriage) - but as a as a spiritual subject.
We do not see our husband or wife as we see other people: he or she is one-off and incomparable. The spouse is past, present and future all at once - and eternally. The spouse is always changing, yet his or her immaterial essence remains the same.
So it is Love which makes for Final Participation in marriage - and in everything else. Love is the primary reality.
Ideal marriage is the model for all human inter-relation with all things. And the further extension of Final Participation is itself therefore though Love - which is why no real work is ever done in science, art, crafts or anything else without Love.