“The kingdom of God has come near. Repent and believe the good news!” Mark 1:15b
There are a few major pieces packed into that one half-verse, and so much of our preaching these days leaves out one bit or another. Second part first. I had a friend in my Jesus people days who bought an old mail truck for his roofing business and personal use, and painted "Repent or Perish" on both sides in large letters. It was uh, recognisable about town. He regretted that a few years later, realising that while it was true as far as it went, it was an incomplete gospel, and thus misleading. He was leaving out the that ye may have eternal (or abundant) life part.
On the other hand, I think the tendency now - perhaps among the young who have attended the best seminaries - is to repeatedly mention that Jesus came to bring Good News and focus on that. Also true as far as it goes, also misleading because it truncates the gospel.
A lot of analysis has gone into the term "Kingdom of God," and my suspiciousness increases the more certain a person sounds that they are explaining to you exactly what this means. Some seem to think it is a thing we apprehend and then enact, others that it is an attitude we are supposed to adopt, while a third might even tell you it is a thing we are supposed to build. Our first impression is usually that it means something like Heaven, or where/how God lives. The verse does say that it has "come near," after all. We think it must at least metaphorically be some sort of place. Other possibilities are that it is a Presence we enter into, or enters into us. All of this is fine, I suppose, none pushing out the others. It's just unwise to settle on one and say "That's it!" I believe it is one of those things placed in elusive territory for us intentionally, so that it can only be understood by both contemplation and action - and you will notice that we cannot contemplate and act very well at the same time, but have to toggle between them. The toggling may be the point.