“Only be strong and very courageous; be careful to do according to all the law which Moses My servant commanded you; do not turn from it to the right or to the left, so that you may have success wherever you go.” (Joshua 1:7 [NASB])
This success is not what we consider as success. It is not rising in the ranks from worker to junior management to upper management. It is not a big salary, elite car, or posh home.
Consider what God imperatively commanded of Joshua. He commanded this of the Israelites, too. God told them to obey His commands that Moses gave them. By doing this, they would succeed.
God knew and we should understand that following Him comes with a cost. That is why He told the Israelites to be strong and courageous. God told them to be resolutely confident and firm in their faith in Him. He knew following Him would need courage. They would need to be steadfast and bold to follow Him, no matter what it costs.
Being God’s children (His people) requires a cost, courage, and confident faith in Him. It definitively gives a reward from Him, too. The reward is the fulfillment of God’s promises to you.
That is the definition of success - you steadfastly following God and His fulfillment of His promises. God only gives good things to His children. He wants the best for each of us. God knows specifically what each of us needs. Often those needs require different things. Whatever the need, God’s filling of that need is success.
Your faithfulness to God, shown by your loving and steadfast obedience and His faithfulness to you, shown by the good gifts - success - given to you, shows the love you have for Him and He for you. It shows your strength and courage in the face of those who set up a stumbling block for you. It shows to them God’s love and faithfulness to you as a shining example of who He is.
God chose the Israelites to be a light on a hill. He chose them to show Him to other nations so that each person would believe in Him. Through the Israelites, God presented His Son as the Messiah, to die for each person’s sins and give each believer in Him forgiveness of those sins and salvation from sin and death. That is the ultimate success God gives. Steadfast and courageous belief in Him in the face of opposition opens the door to receiving the success of good gifts from God that meet our needs and, through us, the needs of other people.
God gives true success to people who are absolutely faithful to Him.
So,
be strong and courageous in obediently following God and He will reward you
with success, receiving person-specific good gifts from Him.