Abraham's sons Isaac and Ishmael represent birth by the Spirit and birth by the flesh (human effort). That which is born of the flesh is enslaved and will not enter God's kingdom. But that which is born of the Spirit will last forever.
This principle exists on both large and small scales. For example, Jesus promised that the gates of hell will not prevail against the church. This promise will come to pass, but it will be as God sends the revival power of his Holy Spirit in response to prevailing prayer–not because Christians develop an ingenious strategy.
This Isaac/Ishmael principle also holds true in our lives. For example, if you're fully given to Jesus, then you will eat, dress, conduct yourself, clean, and speak to others as you're led by the Spirit. There will be no “Ishmael” areas of your life. Likewise, the conversion of others depends primarily on the moving of the Spirit of God–not the way I articulate the gospel, or the expression on my face, and so forth.
Are you in the freedom of God's promises, or are you bound under the law?