In plain words
At once he went to the temple of Īśvara, embraced the Śiva liṅga, and sat repeating the pañcākṣarī mantra, “Om Namaḥ Śivāya, Om Namaḥ Śivāya.” As his span of life ran out, Yama came and cast the noose. When it fell on the Śiva liṅga, Īśvara appeared and rebuked Yamadharmarāja. Pleased with Mārkaṇḍeya's Bhakti, He removed the noose that had wound around him: “Son! Live for ever and flourish,” He said, blessing him. At the very start, Īśvara Himself had granted him a span of 16 years. But later, seeing his Bhakti and surrender, He had to change His own will. By God's grace man can escape even the noose of Yama. The story of the devotee Mārkaṇḍeya is itself a fine example of this. So we must keep thinking of God without a break. Many devotees, in their last days, keep remembering the Name: ‘O Rāma, O Kṛṣṇa, O Govinda...’ As the story of Mārkaṇḍeya proves, in the devotee lies the power that can change God's will.
‘Sarvadā sarvakāleṣu sarvatra haricintanaṃ’
Once, as Yama was going about the world, wherever he looked he saw nothing but devotees. “Wherever I look, people are remembering the Name! How am I to carry these people off?” he wondered, and, caught in a dilemma, he prayed to Īśvara. Then Īśvara appeared: “You may cast your noose on everyone. But it will catch only those who have to undergo the result of karma. It cannot even go near those who have no remainder of karma's result. That is why Mārkaṇḍeya became Mine. I have blessed him,” He said. Nothing is impossible for God. He can grant a boon, and He can cancel the result of karma. So we must not lose heart, thinking the result of karma cannot be escaped, and we must not be afraid. If we pray to God, He wards it off. In this way He has been removing the sufferings of many devotees and granting them happiness and Śānti.