'Sin' is misunderstood in a negative way, as transgression of 'law'. To say 'Jesus was without sin' is therefore a double negative.
A double negative is formulated like: all Men sin, and sin is bad; but Jesus didn't do it, therefore Jesus is good.
But this is inadequate, being both indirect and inaccurate (since a double-negative is not identical-with a positive). We need to know what is the positive statement that this formulation indirectly refers-to.
We need to be able to say that Jesus was wholly-Good - and we need to be able to say what wholly-Good means.
Sin should properly be considered in reference to the positive ideal of being wholly-aligned-with God the creator; being fully in harmony with God's motivations, will etc. in terms of God's ongoing creation.
To be sinful is Not to be aligned with God. Not to be sinful is therefore best thought of as being wholly aligned with God in the work of creation.
Therefore - Jesus was 'without sin' only in a secondary and negative sense of what Jesus was Not. Stated positively, Jesus was wholly aligned with God his Father in terms of God's ongoing work of creation.
To enter Heaven (and for Heaven to remain Heaven) all those in Heaven must be in harmony with God and creation. What Jesus had to do for Man was to enable Men to get into harmony with God, so as to be resurrected and enter Heaven.
This is not a double-negative and roundabout matter of ridding Men of of their sins, but is instead a matter of bringing Men into harmony with God's motivations etc.
By choosing to love and follow Jesus, we become aligned-with God's will; we freely assent to the transformation of resurrection that enables us to enter Heaven.
This is why the Fourth Gospel so often seems to equate 'sin' with 'death'. If we are in a state of sin, we do not want what God wants, therefore we cannot be resurrected and go to Heavenly life eternal: we (our-selves) will therefore die.
And this is why theories of atonement are redundant to the essence of Christianity.