first those verses are not back to back like you posted it.
they are 2 seperate issues.
one The subject: Who then can be saved?
With men this is impossible;but with God all things are possible.
yes you can not be saved without God. with God all things are possible
but the bible also says sinners will not inherit the kingdom.
repent be babtized, believe in the gospel.
second subject- the falling away
now if someone gets saved, recieves the gift of the holy spirit,
had known God, have tasted of the heavenly gift, and about things to come.
those who were once enlightened,
[If they shall fall away]
Luke 8:13 (KJV)
They on the rock are they, which, when they hear, receive the word with joy;
and these have no root, which for a while believe, and in time of temptation fall away.
2 Peter 3:17 (KJV)
Ye therefore, beloved, seeing ye know these things before, beware lest ye also,
being led away with the error of the wicked, fall from your own stedfastness.