Assalaam alaykum. I want to know about the following hadith, but I could not understand what is meant by the 'inhabitants of heaven'. I mean, people do not go to Paradise simply after dying, they have to wait for the Day of Judgement. So, what is meant by 'inhabitants'? Did some people already arrive there?
When Allah loves a servant, He says to Jibreel (Gabriel), “I love so-and-so, so love him,” so Jibreel loves him and then calls out to the inhabitants of heaven, “Allah loves so-and-so, so love him,” and the inhabitants of heaven love him, and then acceptance is placed in the Earth for him.” [Al-Bukhaari and Muslim]

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

The inhabitants of heaven are the angels, as the scholars of Tafseer (Quran exegesis) said in their interpretation of the verse (which means): {And to Allah prostrates whatever is in the heavens...} [Quran 16:49] A hadeeth cited in Musnad Ahmad reads, “...Then Jibreel says, ‘May the mercy of Allah be upon so-and-so.’ The bearers of the Throne say the same, and the ones around them say the same, until the inhabitants of the seven heavens all say it, then it (mercy) descends to Earth for him.”

As-San‘aani wrote:

“The love of the angels has two possible meanings: firstly, it could mean that they ask forgiveness and mercy for the loved person, praise him, and supplicate Allah in his favor. Secondly, it could denote the literal meaning of love among created beings, which is the inclination of the heart towards someone, longing to meet him with affection, and being pleased and content with him. It is deduced from this hadeeth that when a person is loved by people, this indicates the love of Allah for him, as supported by the hadeeth which reads, ‘The angels are the witnesses of Allah in heaven, and you are the witnesses of Allah on Earth.' The hadeeth goes on, 'Then Jibreel calls out to the inhabitants of heaven, saying, ‘Allah loves so-and-so; so love him!’ So the inhabitants of heaven love him, and acceptance is placed in the Earth for him.” [At-Tahbeer]

Allah knows best.