Verse 24 is one of the exhortations(Verse 22-23) of the author to his readers, grounded in Christ’s accomplishments for us in verses 19-21.
Here is one good example of how translations tend to leave out some nuances from the original language. A literal translation, though a bit awkward in english, is more likely to capture what the author was saying. Literally it can be read like this : ” let us consider one another into agitation of love and of good works”. The direct object or receiver of the action κατανοῶμε is the personal pronoun “one another”. This is thinking of intentionally loving and doing good to one another. You are literally provoking yourself to love and be loved.
To obey this command, we would need the company of other believers, for it is impossible to love one another in this sense if you are not “with” one another. Yes we can still remotely do good to others, but what this verse is telling us implies togetherness. That’s why in verse 25, the means by which this is brought about is by being with each other.
First it’s stated negatively(not neglecting). Perhaps because of persecution, some were in the habit of not attending the meetings. It is remarkable that in our own day, the excuses given to justify our habits of neglecting our own meetings are very superficial, unreasonable and selfish. None of us were persecuted the way the first century Christians were, yet even then, it is not enough to justify their own reluctance to come.
Then in verse 25c, he stated it positively (encouraging each other). By doing this, the author made it clear that it is not enough to be there in the fellowship. One must engage actively in the ministry of encouragement. The principle applies to our weekly corporate worship also, but contextually this is talking more about small group meetings.
Instead of habitual neglect, we must meet even more so as we see the day of Christ’s coming drawing near. There’s a progression here. It is not a matter of mainting a meeting once a week. It is a matter of making this meetings more frequent. As the day approches, the love of many will grow cold. And how do we nourish our love for others? How do we fight this coldness? It is by being with each other!