Enriching Our Understanding of Baptism from Deuteronomy and Joshua

Deut 31:5–6
The LORD will give them over to you, that you may do to them according to every commandment which I have commanded you. Be strong and of good courage, do not fear nor be afraid of them; for the LORD your God, He is the One who goes with you. He will not leave you nor forsake you.”

Matt 28:18–20
Then the eleven disciples went away into Galilee, to the mountain which Jesus had appointed for them.  When they saw Him, they worshiped Him; but some doubted. And Jesus came and spoke to them, saying, “All authority has been given to Me in heaven and on earth. Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you; and lo, I am with you always, even to the end of the age.” Amen.

Josh 1:5–9
No man shall be able to stand before you all the days of your life; as I was with Moses, so I will be with you. I will not leave you nor forsake you. Be strong and of good courage, for to this people you shall divide as an inheritance the land which I swore to their fathers to give them. Only be strong and very courageous, that you may observe to do according to all the law which Moses My servant commanded you; do not turn from it to the right hand or to the left, that you may prosper wherever you go. This Book of the Law shall not depart from your mouth, but you shall meditate in it day and night, that you may observe to do according to all that is written in it. For then you will make your way prosperous, and then you will have good success. Have I not commanded you? Be strong and of good courage; do not be afraid, nor be dismayed, for the LORD your God is with you wherever you go.”

When we line these texts up together, we can see how Moses leaving Joshua behind is the background for the language of what has often been called the "Great Commission." Only now, instead of conquering all the nations, the mission is to make disciples of them. Just a few things to note as we compare the passages:

The strengthening and encouragement of baptism. "Some doubted," Matthew tells us. Surely, based upon the repeated commands to be strong and courageous, Joshua and the people must have been tempted to doubt. The evangelist tells us that Jesus responded to this doubting with Word and sacrament. 

The Word is His declaration that all authority in heaven and earth belongs to Him. And then He puts a sign of that authority, the seal of the covenant/kingdom, upon everyone whom He separates into His church from those nations: baptism. Our baptisms announce that Jesus, Who possesses all celestial and earthly authority, has claimed a special authority over us. 

The place of commandments in the Christian life. Many Christians are uneasy about the language of obedience and commandments. Some of that is good—we must renounce any idea that our obedience to commandments is worthy of any reward or praiseworthy to be proud of it. But if we are resistant to the idea that commandments are central to the Christian life, then we are resistant to Christ's own version of Christianity. 

Just as the path of enjoyment of the blessing unto which God had saved Israel was the path of obedience to God's commandments, so also as Jesus sends the apostles into the world to bring about the nations' enjoyment of the blessing unto which He has saved us, Jesus says "teaching them to observe all things that I have commanded you." Recognizing Jesus as the Triune God of the Bible, and that all sound biblical commandments are His, is a core component of Christianity. 

And we see here that He attaches it to our baptism. Our baptism is designed to strengthen and encourage our faith in Him. But it also presses upon each of us Christ's rightful demand to complete, exhaustive obedience to Him.

The source of strength in the Christian life: God has given us Himself. In the Old Testament context, the LORD promised His own fellowship to attend Joshua and Israel upon their mission and in their obedience. Here, we see that Jesus Himself is Yahweh, Who is with us. The Spirit is His Spirit. Jesus is with us always not only by way of His divine nature, in which He fills all in all, but also in His Spirit's mediating unto us His presence and fellowship as the risen Redeemer, the God-Man. 

Thus by giving us this Triune Name (singular name, not plural!) by which to be baptized into the name of Jesus Christ, Jesus assures us that we who look to Him in faith have His constant accompaniment by His Spirit. The Father is with us in the Son, and the Son is with us in the Spirit. Here is the strength and comfort and joy of the Christian as he lives out a life of consecrated obedience: "and lo, I am with you always, even to the end of the age."