As the mission of God unfolds in the Old Testament, he enters into covenant relationship with key partners is mission. In each of these covenant relationships there are both missional and formational components, and they are closely related.
Abraham
God chose to be a central player in his unfolding strategy for redeeming the world. In Genesis 12:1-3 we read:

Now the LORD said to Abram, “Go from your country and your kindred and your father’s house to the land that I will show you. I will make of you a great nation, and I will bless you, and make your name great, so that you will be a blessing. I will bless those who bless you, and the one who curses you I will curse; and in you all the families of the earth shall be blessed.”

God did not only use Abraham in fulfillment of his plans, however. The Lord also transformed Abraham in the process. In Genesis 15, for example, God revealed to Abraham that his heir will be his own son, even though this was impossible given his wife’s old age. He chose to believe what God said, and God  “reckoned it to him as righteousness” (15:6). God worked with Abraham to help him grow in a trusting relationship.
Then, in Genesis 17, the Lord revealed to Abraham more of his grand plan. God promised to give Abraham many descendants and to place them in a special land. Abraham’s part in this covenant relationship was to make sure that every male in his household was circumcised, including Abraham. His obedience showed an exceptional quality of devotion to God. (I’ve sometimes wondered how difficult it would be to get male converts to Christianity if conversion was necessarily followed by circumcision rather than baptism!)
Genesis 18 shows a curious dimension of the Lord’s relationship with Abraham. When God reveals his plans to destroy Sodom because of its wickedness, Abraham argues with God, appealing for mercy for Sodom. This shows how Abraham has grown in boldness with God, and perhaps also in compassion.

Perhaps the most striking incident that reveals the Lord’s shaping of Abraham is in Genesis 22, when God tells Abraham to sacrifice Isaac on one of the mountains in the land of Moriah. We can only imagine Abraham’s inner turmoil as he led his son to what seemed to be his death. Abraham’s faith in God was tested to an extreme degree and he passed the test with flying colors. Since the Lord knew Abraham’s heart even before the incident on the mountain, I can only conclude that this test of faith was for Abraham’s growth. (Picture: Rembrandt’s painting of the Sacrifice of Isaac, 1635.)
With the examples I mentioned here, we see how God was in the process of forming Abraham’s soul even as he was using him in the unfolding of his mission to redeem the world.
Moses
In the life of Moses we see a similar intermingling of missional and formational. It began when the Lord revealed himself to Moses at the burning bush, calling him to return to Egypt to set Israel free from bondage. When Moses protested that he was not up to the job, a fascinating conversation ensued, in which the Lord condescended to work with Moses’ fears and insecrutities, while building his confidence both in God and in himself (see Exodus 3).
Later, after Moses had been used by God to lead the Israelites out of Egypt, they were attacked in the wilderness by the Amalekites. When the Israelites defended themselves, they were successful, but only as long as Moses held up his staff. When his arm became weakened, and he lowered his staff, the Israelites would begin to lose. So Moses, who had become quite a strong and solitary leader, learned to depend on others for help (see Exodus 17).
Then, in the next chapter, Moses was visited by his father-in-law, Jethro.  He observed his son-in-law working morning to night judging the Israelites’ petty disputes. Speaking frankly to Moses, Jethro said, “What you are doing is not good. You will surely wear yourself out, both you and these people with you. For the task is too heavy for you; you cannot do it alone” (18:17-18). Jethro went on to suggest that Moses appoint trustworthy men to judge the minor cases, leaving only Moses as the “Supreme Court” of Israel. Moses received his father-in-law’s counsel and delegated much of his judging to others. I wonder if the experience of getting help from his assistants in holding up his staff prepared Moses to take the steps recommended by Jethro.
At any rate, Exodus shows us how God not only used Moses, but also shaped him as a leader and a man of faith. This kind of missional-formational combination is seen throughout the Old Testament, not only with the leaders of Israel, but also with the Israelites themselves.