“And in the morning, rising up a great while before day, he went out, and departed into a solitary place, and there prayed.”
Very early in the morning, while it was still dark, Jesus got up, left the house and went off to a solitary place, where he prayed — the most intensely active day of public ministry in Mark is followed by pre-dawn solitary prayer before the next day begins. The solitary place (erēmos topos, the same word as wilderness) is Jesus' consistent retreat from the demands of public ministry. The pattern is significant: the kingdom flows from prayer, not the reverse. The public ministry — teaching, exorcism, healing, crowds at the door — is preceded by the wilderness testing and followed by pre-dawn communion with the Father. The prayer is not described, but its purpose is evident: the direction for the next phase comes from the Father.
Church Fathers on Mark 1:35
After that the Lord had cured the sick, He retired apart.
But by this preaching, which, he says, 'He continued in all Galilee,' is also meant the sermon of the Lord delivered on the mount, which Matthew mentions, and Mark has entirely passed over, without giving any thing like it, save that he has repeated some sentences not in continuous order, but in scattered places, spoken by the Lord at other times.
Again, mystically if by the setting of the sun, the death of the Saviour is intended, why should not His resurrection be intended by the returning dawn? For by its clear light, He went far into the wilderness of the Gentiles, and there continued praying in the person of His faithful disciples, for He aroused their hearts by the grace of the Holy Spirit to the virtue of prayer.