In the gospel of John in particular we meet that phrase often: believe in Jesus (e.g., Jn 3.16)
However, the problem with the translation 'in' is that it can so easily be misunderstood to mean believing certain things about Jesus and that's all. Of course, it is critical that we do believe things about Jesus Christ because they are foundational to believing in Him.
If we don't believe that Jesus is the Son of God (Jn 20.31) then our belief in Him will be defective.
If we don't believe that He has settled the unrighteousness of world's sin (Jn 1.29) by bearing it away from us then we will scarcely know why Jesus' coming as the Man is even important for our lives.
Nevertheless, on knowing these things, it is still possible to remain outside God's salvation. To believe in Jesus = to believe into Him implying commitment, trust in Him; just as I am trusting the chair I am sitting on will hold me up.
Hence, believing in Jesus means to rely on him for salvation. Those who are lost in some way are rescued. That's what all of those who have turned to Christ in repentance by committing their hearts and lives to Him have been: rescued.
Rescued from the penalty of sin because final consequences of sin's rebellion is eternal life; rescued from the power of sin in this present life; and finally, rescued from the presence of sin when Christ returns in all his glory.
