The gospel of the Kingdom is simple:
The Kingdom of God is within you! And you are saved by grace through faith - faith that God is your Father and you are His son/daughter and that your eternity is secured. And faith that causes you to surrender your all to Him and causes you to show LOVE. That's what Jesus taught - in essence.
(Within you - for the spirit of the Father is already in you. This spirit comes at the age of accountability, usually between 4 and 6 years of age.)
Salvation comes to you when you surrender your heart completely to God as a result of a personal experience of the quickening impact of the love of God. This can happen through many different ways.
The quickening, spiritual life-giving love of God can be embraced by a mortal at the foot of the cross. It can also be embraced through many other ways. Jesus never ever limited it to the cross. This explains why He forgave sins and got people born again (born of water and of the spirit) and added them to the Father's Kingdom before he was crucified.
I am sharing some deep stuffs here. Without the Spirit of Truth, you may not appreciate what I am saying. To understand salvation clearly, you have to focus more on the teachings of Jesus Himself - not the teachings of your Imam, Priest, Pastor or St. Peter or St. Paul.
This message of salvation is applicable to all, regardless of their religious background and their planet of origin.
A major mistake a lot of people make is this: they define salvation based on their own individual experience. Life is so, so big and vast. The truth far transcends the very limited and greatly circumscribed experiences of one, two or a few individuals.
Jesus never narrowed down salvation. He taught a gospel of salvation that is readily available and applicable to Jews, Christians, Muslims, etc and also to humans on other planets.
A major problem with the prominent religions or faiths on our planet is this: they succumb to the temptation of narrowing down salvation to members of their faith or religion. In some cases it's so bad that salvation is greatly narrowed down to accommodate only members of a particular church or temple - a subset of a faith.
For example, Christianity. Some christian sects or churches have further narrowed salvation down to such a level that except you become a member of their church and accept the doctrines of their church, you shall never be saved. It's that pathetic...
No human being; no church; no faith or religion; no experience of a single individual or group has a monopoly on God. None.