Swami Krishnananda explains:
''The story of the amritam manthana in the Bhagavata is only an allegory of the search for the nectar of immortality in spiritual life. In the beginning, only poison comes. Nectar did not come in the beginning. The Devas and Asuras were churning. With great effort they were trying to get the nectar, but terrific halahala kalakuta visha came up. When you ask for God, God will not come in the beginning. You will only get a devil first, so do not expect to get nectar in the beginning. The horrific, satanic obstacle will come first. That is the halahala visha, poison, which was really intolerable, and nobody could face it.
The first thing that you face in spiritual life is opposition and confusion of thought, tension of consciousness, pain of every kind, frustration, and defeatism, which result in a repulsion from spiritual pursuits. You will go back home as if nothing has happened. This is the poison that is coming, halahala. But the Devas and Asuras did not leave like that. Let the poison come. They gave it to Lord Siva: "Please drink it on our behalf." God Himself will take care of us. It means that. When the poison comes, you need not be afraid of it. God will take care of you. He will protect you even from that halahala kalakuta poison. Daivī hy eṣā guṇamayī mama māyā duratyayā, mām eva ye prapadyante māyām etāṃ taranti te (BG 7.14): If you resort to Him, He will take care of you. Let the visha, the poison, the snake or the cobra come. He will see that it is taken care of. Many were bitten by the cobra of desire, and many were faced with the halahala visha of worldly tension and agony, but they were all solved, and they all vanished like mist before the sun.
So persistence is essential. When we are faced with problems, oppositions, ill will, tension and suffering of any kind, we should not take to our heels. If the Devas and Asuras had run away in fear when the visha came, then they would have lost the nectar also, but after the visha went away, wonderful gems, ratna, and so much more came up. That is the eight siddhis – anima, mahima, laghima, garima, prapti, etc. – that we hear of. The wonderful siddhis are the ratnas that come out from the ocean of nectar when we churn it by the power of sadhana.
Then finally Dhanvantari comes with a pot of nectar; that is the immortality, the ambrosia that will face us.
First is opposition between God and devil. The Devas and Asuras are fighting terribly, killing each other. That is the first stage of life. Then the higher one is a co-operation between ourselves: "Don't fight. Let us all work together for spiritual purposes." But when we work together, we get poisoned. That is the second experience. Even then, we should not leave it. When even the poison and troubles are faced honestly and with dedication of oneself to God, we will get eight siddhis. There are so many siddhis mentioned in the Bhagavata. Even the siddhis are only obstacles finally, though they are much greater than earthly riches. When even these ratnas are rejected, and we want only the nectar in the end, then the fourteenth gem comes. That is the nectar of ambrosia, immortality.
So we should never budge until we get it. Until God comes, we shall not leave the pursuit of God.''
[source: https://www.swami-krishnananda.org/disc/disc_269.html]