I fear? the LORD is the strength of my life;
of whom shall I be afraid? Psa 27:1
The LORD is my rock, and my fortress, and my deliverer; my God, my strength, in whom I will trust; my buckler, and the horn of my salvation, and my high tower. Psa 18:2
In our earthly pilgrimage, we need strength to stay on course. The world, the flesh, and the devil want to prevent us from progressing down the Lord's perfect path. David found in the Lord the strength for this need as well. "It is God who arms me with strength, and makes my way perfect". Psa 18:32
At times, when walking along our designated path of life, we get trapped in circumstantial nets, laid by the enemy of our souls. When David experienced these traps, he cried out to God for the necessary strength. "Pull me out of the net which they have secretly laid for me, For You are my strength" Psa 31:4
At other times along our path, the problem is not a trap, but an all-out battle. Once again, David found the strength he needed in His Lord. "For You have armed me with strength for the battle; You have subdued under me those who rose up against me" Psa 18:39
Sometimes, the need for strength pertains to what is going on within (or flowing forth from within). The thoughts we are thinking, and the words we are expressing might need to be anchored again in the will of the Lord. David also knew how to turn to God for this essential strength as well. "Let the words of my mouth and the meditation of my heart be acceptable in Your sight, O LORD, my strength and my redeemer" Psa 19:14
When he weakened within and stumbled in failure, David still knew where to turn for the only help that will ever prove sufficient. "My flesh and my heart fail; But God is the strength of my heart and my portion forever" (Psa_73:26). Source: Day by Day by Grace
Charles H. Spurgeon
Psalm 18:2
Note: I am not a Calvanist-but will give credit, where credit is due; Calvin said some things that deserve to be quoted.