The first formula, which precedes the other three and is simply being, states: 'Acknowledge BEING for what it is.'
But BEING has three, supreme internal relationships, or forms, reality, ideality, and morality, in all of which it must be acknowledged. Hence three supreme imperative formulas.
Ideal being (ideality), which is itself light, reveals the other two. Through it we know real beings, which indicate in us the first imperative formula: 'Acknowledge real beings for what they are', that is, 'Esteem beings, love them, help them; rejoice in the being that they have, and desire for them the being they require according to their nature, and which perfects them.'
When we acknowledge moral being, that is, the essentially moral will, the will of God, the second moral imperative reveals itself in our spirit as: 'Make your will one with the essentially moral will.'
After making known real being and moral being, ideal being finally makes itself known by reflection as truth and gives rise to the third imperative which states: 'Acknowledge ideal being,' or 'Esteem the truth unreservedly,' or 'Follow the light of reason.'
All four formulas are equally supreme, but the three last are contained in the first, which is perfected by each of them.
[Antonio Rosmini, Conscience, Denis Cleary and Terence Watson, trs., Rosmini House (Durham: 1989) p. 92 [190-4], sections 191-193.] Like much of Rosmini, I find this approach to natural law an intriguing one, but am not really sure how it lines up with anything else. The basic idea is clear enough, though: the three 'internal relationships' are transcendental attributes of being (reality, goodness, truth), and it's unsurprising that Rosmini makes being the principle of morality, given how he understands its role in our cognition.