In short
Two views of what the opening of heaven during the baptism of Jesus signified:
It was a sign that a divine revelation was about to occur (see Isaiah 64:1).
It alluded to the restoring of communion between God and man (John 1:51; Revelation 4:1, Revelation 19:11).
Interpretation 1:
The opening of the heavens during the baptism of Jesus was a sign that a divine revelation was about to occur (see Isaiah 64:1).1
Interpretation 2:
The opening of the heavens during the baptism of Jesus testifies to the restoration of the communion between God and man (John 1:51; Revelation 4:1, Revelation 19:11)2.
16 And when Jesus was baptized, immediately he went up from the water, and behold, the heavens were opened to him, and he saw the Spirit of God descending like a dove and coming to rest on him;