I am always stuck by the simplicity of Jesus' messages. His gently directs his listeners to take clear steps of faith that would move them ever closer to their God. In doing so the He emphasized a changed direction, perspective and condition of the mind, body and soul. His words are full of exhortation , not condemnation.
From that time Jesus began to preach and to say, “ Repent, for the kingdom of heaven is at hand.” Matt 4:17
His encouragement is not to do works but to "think differently" a change of mind (repent) from doing works of sin to face the kingdom that is before them, Jesus being the kingdom. In Mark's Gospel "belief" in the Gospel being preached is added to the change of mind (Mk 1:15).
But seek first the kingdom of God and His righteousness, and all these things shall be added to you. Matt 6:33
Turn your focus away from cares and needs is His encouragement and in place of that turn your focus on the kingdom. Added to that a seeking of His righteousness. The seeking of His righteousness is the alternative to seeking our own righteousness. His righteousness comes by faith and not works.
and said, “ Assuredly, I say to you, unless you are converted and become as little children, you will by no means enter the kingdom of heaven. Therefore whoever humbles himself as this little child is the greatest in the kingdom of heaven. Matt 18:3-4
"Converted" is the Greek word "strepho" that means, to turn around, a change of direction. The change direction is a change attitude with the humble nature of a child being the desire. Possessing such a changed attitude opens wide the kingdom doors.
So its a changed mind, a changed focus, and a changed direction with a changed attitude that ushers the sinner into God's kingdom. Can it be any simpler? It is an inner transition and not an outer work. It is an act of belief and trust in the righteousness of God and not our own which Isaiah says , "are as filthy rags" (Isa 1:6). Its belief in Him and not in us or in the things of this world.