What did God know when He sent Hagar back to Sarah's tent?

God knew that thirteen years later He would tell Hagar and Ishmael to go right back to the desert, the same place He had brought her from when He first intervened. He knew the future return, even while instructing her to stay in Sarah’s tent.

Les teaches that when Hagar was first pregnant, she began taunting Sarah and making life miserable for her. Sarah finally went to Abraham and demanded he get rid of Hagar. Abraham sent her away, but God intervened in the desert. God told Hagar to go right back to Sarah’s tent and stay there. Les then asks what God knew: thirteen years later, God would tell Hagar and Ishmael to go right back where He had brought her from in the first place, out in the desert. This fits the Galatians 4 picture, where Isaac and Ishmael illustrate the flesh persecuting the Spirit, and Scripture says to cast out the bondwoman and her son. Les identifies the bondwoman and her son as picturing the Law and legalism. So God’s instruction to return was not the end; He knew the later expulsion and the desert destination.

What did God already know when He told Hagar to return to Sarah's tent?

God already knew that thirteen years later He would instruct Hagar and Ishmael to leave and return to the desert, the very place He had brought her from. The command to return to Sarah's tent was temporary, setting the stage for that later departure.