By the theological virtue of Divine Faith! This is a supernatural Gift of God which no human being can obtain on his/her own. Since the Grace of God builds on the order of nature which He Created, Faith in no way contradicts nature, but rather, builds on it leading to the Infinite where it transcends nature. It is, first and foremost, a gratuitous work of God. But God invites us to freely respond to it by accepting His Grace, i.e. the Life of God in us, in order to continuously grow with His Divine Life in us. This is a result of our free will given to us by God, Who will not force it. In other words, Heaven can and should begin here and now on earth in us, both corporately (the Church) and individually, but we will only experience it's fullness at the "close of the ages" when we see God "face to face" and all Creation is consummated and brought to the Eternal Father by His Son. Individually, this could mean at our death, but the hereafter is still a mystery to us and I don't think any of us know all the details. I mean by this that we will have a share in God's Eternity and concepts of "time" and "space" in such a situation would obviously be much different than our experience of them in our "life of the flesh".
I cannot judge other people, only pray for them and open myself to God to allow Him to work through me to bring others to the Faith. Because it is a lifelong process, no one knows just how or when the Grace of God will work in them to bring them to Grace, or whether or not they will accept that Grace.