"But I do not account my life of any value nor as precious to myself, if only I may finish my course and the ministry that I received from the Lord Jesus, to testify to the gospel of the grace of God. And now, behold, I know that none of you among whom I have gone about proclaiming the kingdom will see my face again... And now I commend you to God and to the word of his grace, which is able to build you up and to give you the inheritance among all those who are sanctified... You yourselves know that these hands ministered to my necessities and to those who were with me. In all things I have shown you that by working hard in this way we must help the weak and remember the words of the Lord Jesus, how he himself said, 'It is more blessed to give than to receive.' And when he had said these things, he knelt down and prayed with them all. And there was much weeping on the part of all; they embraced Paul and kissed him, being sorrowful most of all because of the word he had spoken, that they would not see his face again. And they accompanied him to the ship." - Acts 20:24-25, 32, 34-38 ESV
Paul is sure that God's grace is able to give us two things. It is able to build us up and it is able to give us a joint inheritance. Now and Later are covered.
Paul knew He wasn't coming back but He also knew that the words He had spoken to these people had been about Christ. The Gospel of Grace had been given. He had explained thoroughly about Jesus in the Hebrew scriptures and about the cross. He had explained the free gift of salvation dozens of ways. He wasn't like other teachers that demanded tribute. He wasn't securing a following for himself for security or financial gain so that if he came back this way as he traveled some scholarly teaching circuit he would have connections in this city. He wasn't networking. He was loving God and working with his hands as he labored in the word.
There may be people who are only in your life for a short season. I feel that way on Saturdays when we talk to people about life, death, Heaven and Hell. I may never see them again but in a moment I (we) can give them something eternal. We don't offer a momentary smile like an entertainer does... smiles are great but they are like flowers that fade. We offer a Savior who saves and sticks closer than a brother long after we leave the scene.
Are people just in our lives so we can get something from them or is it an opportunity to give something eternal away?
Grace is able to build up. Grace is able to give an 'inheritance among all those who are sanctified' and that is precious beyond imagining.