How do angels (messengers of God) come and go when they minister to God? It was my question and the following will be a good answer to it.
In the Bible, we are told that angels used a stairway (or ladder) to travel between heaven and earth (Genesis 28:10-15).10 Jacob left Beersheba and set out for Haran.
11 When he reached a certain place, he stopped for the night because the sun had set. Taking one of the stones there, he put it under his head and lay down to sleep.
12 He had a dream in which he saw a stairway resting on the earth, with its top reaching to heaven, and the angels of God were ascending and descending on it.
13 There above it stood the LORD, and he said: "I am the LORD, the God of your father Abraham and the God of Isaac. I will give you and your descendants the land on which you are lying.
14 Your descendants will be like the dust of the earth, and you will spread out to the west and to the east, to the north and to the south. All peoples on earth will be blessed through you and your offspring.
15 I am with you and will watch over you wherever you go, and I will bring you back to this land. I will not leave you until I have done what I have promised you."
Jesus said to Nathanael “I tell you the truth, you shall see heaven open, and the angels of God ascending and descending on the Son of Man” (John 1:51).
Heaven open - This is a figurative expression, denoting "the conferring of favors." Psalm 78:23-24; "he opened the doors of heaven, and had rained down manna." It also denotes that God was about to work a miracle in attestation of a particular thing. See Matthew 3:16. In the language, here, there is an evident allusion to the ladder that Jacob saw in a dream, and to the angels ascending and descending on it, Genesis 28:12. It is not probable that Jesus referred to any particular instance in which Nathanael should literally see the heavens opened. The baptism of Jesus had taken place, and no other instance occurred in his life in which it is said that the "heavens were" opened.
Angels of God - Those pure and holy beings that dwell in heaven, and that are employed as ministering spirits to our world, Hebrews 1:14. Good men are represented in the Scriptures as being under their protection, Psalm 91:11-12; Genesis 28:12. They are the agents by which God often expressed his will to men, Hebrews 2:2; Galatians 3:19. They are represented as strengthening the Lord Jesus, and ministering unto him. Thus they aided him in the wilderness Mark 1:13, and in the garden Luke 22:43, and they were present when he rose from the dead, Matthew 28:2-4; John 20:12-13. By their ascending and descending upon him it is probable that he meant that Nathanael would have evidence that they came to his aid, and that he would have "the" kind of protection and assistance from God which would show "more fully that he was the Messiah." Thus his life, his many deliverances from dangers, his wisdom to confute His skilled and cunning adversaries, the scenes of his death, and the attendance of angels at his resurrection, may all be represented by the angels descending upon him, and all would show to Nathanael and the other disciples most clearly that he was the Son of God.