As for what is maintained in these tantras:
In krīya we are inferior and the gods supreme.
We are like servants, and the deities are the masters.
By practicing in that style, the siddhis are received.
In charya we view ourselves and the gods as being equal.
We are samayasattva, the deity jñanasattva.
The deity occupies the space in front of us.
Siddhi is received in the style of two friends.
In yoga while the two are actually non-dual,
The god is summoned to union and afterward dismissed.
Siddhi is received like water poured into water.
In kriya tantra, the jñanasattva deity is said to be like a king. We, as servants, hope to receive siddhi. The Tantra of Receiving the Siddhis of all the Families (rigs thams cad pa’i dngos grub len pa’i rgyud) says:
The lord is viewed with the body of a king.
We have a perception of ourselves as servants.
Siddhi, which is the essence of mantra practice,
Is received with unsurpassable excellence.
As for upa tantra, in front of the samayasattva, our visualization of the deity, we receive siddhi from the jñanasattva deity, visualized as a friend or companion. The General Tantra of the Three Families says:
With the deity as friend or companion
Ultimate siddhi is to be received.
In yoga tantra, we meditate on ourselves in yogic union with the deity. The jñanasattvas of union are drawn in and dissolve into us. By sealing with the four mudras and so on, even when the offerings, praises, recitation, and so forth are over, we ask them to depart. At the time of the non- duality of the main part, siddhi is said to arise. The Vajra Arising (rdo rje ‘byung ba) says:
We receive non-dual Dharmadhatu
And the highest ultimate siddhi.
We are blessed with the tathagata, padma, and vajra families of the external mantra, sealed with the samaya, Dharma, karma, and mahamudras.